diff --git a/dev/core/src/com/google/gwt/dev/GWTCompiler.java b/dev/core/src/com/google/gwt/dev/GWTCompiler.java
index d851ff8..98fae9a 100644
--- a/dev/core/src/com/google/gwt/dev/GWTCompiler.java
+++ b/dev/core/src/com/google/gwt/dev/GWTCompiler.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2007 Google Inc.
+ * Copyright 2008 Google Inc.
  * 
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not
  * use this file except in compliance with the License. You may obtain a copy of
@@ -36,8 +36,8 @@
 import com.google.gwt.dev.jdt.StandardSourceOracle;
 import com.google.gwt.dev.jdt.WebModeCompilerFrontEnd;
 import com.google.gwt.dev.jjs.JJSOptions;
-import com.google.gwt.dev.jjs.JsOutputOption;
 import com.google.gwt.dev.jjs.JavaToJavaScriptCompiler;
+import com.google.gwt.dev.jjs.JsOutputOption;
 import com.google.gwt.dev.shell.StandardRebindOracle;
 import com.google.gwt.dev.util.DefaultTextOutput;
 import com.google.gwt.dev.util.SelectionScriptGenerator;
@@ -51,6 +51,7 @@
 import com.google.gwt.dev.util.log.PrintWriterTreeLogger;
 import com.google.gwt.dev.util.xml.ReflectiveParser;
 import com.google.gwt.util.tools.ArgHandlerDisableAggressiveOptimization;
+import com.google.gwt.util.tools.ArgHandlerEnableAssertions;
 import com.google.gwt.util.tools.ArgHandlerExtra;
 import com.google.gwt.util.tools.ArgHandlerFlag;
 import com.google.gwt.util.tools.ArgHandlerOutDir;
@@ -335,6 +336,8 @@
 
     registerHandler(new ArgHandlerScriptStyle(jjsOptions));
 
+    registerHandler(new ArgHandlerEnableAssertions(jjsOptions));
+
     registerHandler(new ArgHandlerDisableAggressiveOptimization() {
       @Override
       public boolean setFlag() {
diff --git a/dev/core/src/com/google/gwt/dev/GWTShell.java b/dev/core/src/com/google/gwt/dev/GWTShell.java
index 9080797..ea48b17 100644
--- a/dev/core/src/com/google/gwt/dev/GWTShell.java
+++ b/dev/core/src/com/google/gwt/dev/GWTShell.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2007 Google Inc.
+ * Copyright 2008 Google Inc.
  * 
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not
  * use this file except in compliance with the License. You may obtain a copy of
@@ -36,6 +36,7 @@
 import com.google.gwt.dev.util.arg.ArgHandlerScriptStyle;
 import com.google.gwt.dev.util.log.AbstractTreeLogger;
 import com.google.gwt.util.tools.ArgHandlerDisableAggressiveOptimization;
+import com.google.gwt.util.tools.ArgHandlerEnableAssertions;
 import com.google.gwt.util.tools.ArgHandlerExtra;
 import com.google.gwt.util.tools.ArgHandlerFlag;
 import com.google.gwt.util.tools.ArgHandlerOutDir;
@@ -450,6 +451,8 @@
 
     registerHandler(new ArgHandlerScriptStyle(jjsOptions));
 
+    registerHandler(new ArgHandlerEnableAssertions(jjsOptions));
+
     registerHandler(new ArgHandlerDisableAggressiveOptimization() {
       @Override
       public boolean setFlag() {
diff --git a/dev/core/src/com/google/gwt/dev/jjs/JJSOptions.java b/dev/core/src/com/google/gwt/dev/jjs/JJSOptions.java
index 879e1d5..a689917 100644
--- a/dev/core/src/com/google/gwt/dev/jjs/JJSOptions.java
+++ b/dev/core/src/com/google/gwt/dev/jjs/JJSOptions.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2007 Google Inc.
+ * Copyright 2008 Google Inc.
  * 
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not
  * use this file except in compliance with the License. You may obtain a copy of
@@ -21,6 +21,7 @@
 public class JJSOptions {
 
   private boolean aggressivelyOptimize = true;
+  private boolean enableAssertions = false;
   private JsOutputOption output = JsOutputOption.OBFUSCATED;
   private boolean validateOnly = false;
 
@@ -33,6 +34,7 @@
 
   public void copyFrom(JJSOptions other) {
     this.aggressivelyOptimize = other.aggressivelyOptimize;
+    this.enableAssertions = other.enableAssertions;
     this.output = other.output;
     this.validateOnly = other.validateOnly;
   }
@@ -52,6 +54,13 @@
   }
 
   /**
+   * Returns true if the compiler should generate code to check assertions.
+   */
+  public boolean isEnableAssertions() {
+    return enableAssertions;
+  }
+
+  /**
    * Returns true if the compiler should run in validation mode, not producing
    * any output.
    */
@@ -67,6 +76,13 @@
   }
 
   /**
+   * Sets whether or not the compiler should generate code to check assertions.
+   */
+  public void setEnableAssertions(boolean enableAssertions) {
+    this.enableAssertions = enableAssertions;
+  }
+
+  /**
    * Sets the compiler output option.
    */
   public void setOutput(JsOutputOption output) {
diff --git a/dev/core/src/com/google/gwt/dev/jjs/JavaToJavaScriptCompiler.java b/dev/core/src/com/google/gwt/dev/jjs/JavaToJavaScriptCompiler.java
index 512fe02..0ab0875 100644
--- a/dev/core/src/com/google/gwt/dev/jjs/JavaToJavaScriptCompiler.java
+++ b/dev/core/src/com/google/gwt/dev/jjs/JavaToJavaScriptCompiler.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2007 Google Inc.
+ * Copyright 2008 Google Inc.
  * 
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not
  * use this file except in compliance with the License. You may obtain a copy of
@@ -32,6 +32,7 @@
 import com.google.gwt.dev.jjs.ast.JProgram;
 import com.google.gwt.dev.jjs.ast.JReferenceType;
 import com.google.gwt.dev.jjs.impl.ArrayNormalizer;
+import com.google.gwt.dev.jjs.impl.AssertionNormalizer;
 import com.google.gwt.dev.jjs.impl.AssertionRemover;
 import com.google.gwt.dev.jjs.impl.BuildTypeMap;
 import com.google.gwt.dev.jjs.impl.CastNormalizer;
@@ -307,9 +308,14 @@
       // 
       checkForErrors(logger, true);
 
-      // TODO: figure out how to have a debug mode.
-      boolean isDebugEnabled = false;
-      if (!isDebugEnabled) {
+      /*
+       * TODO: if we defer this until later, we could maybe use the results of
+       * the assertions to enable more optimizations.
+       */
+      if (options.isEnableAssertions()) {
+        // Turn into assertion checking calls.
+        AssertionNormalizer.exec(jprogram);
+      } else {
         // Remove all assert statements.
         AssertionRemover.exec(jprogram);
       }
@@ -365,9 +371,6 @@
       // (5) "Normalize" the high-level Java tree into a lower-level tree more
       // suited for JavaScript code generation. Don't go reordering these
       // willy-nilly because there are some subtle interdependencies.
-      if (isDebugEnabled) {
-        // AssertionNormalizer.exec(jprogram);
-      }
       CatchBlockNormalizer.exec(jprogram);
       CompoundAssignmentNormalizer.exec(jprogram);
       JavaScriptObjectCaster.exec(jprogram);
diff --git a/dev/core/src/com/google/gwt/dev/jjs/impl/AssertionNormalizer.java b/dev/core/src/com/google/gwt/dev/jjs/impl/AssertionNormalizer.java
new file mode 100644
index 0000000..0120829
--- /dev/null
+++ b/dev/core/src/com/google/gwt/dev/jjs/impl/AssertionNormalizer.java
@@ -0,0 +1,84 @@
+/*
+ * Copyright 2008 Google Inc.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.google.gwt.dev.jjs.impl;
+
+import com.google.gwt.dev.jjs.ast.Context;
+import com.google.gwt.dev.jjs.ast.JAssertStatement;
+import com.google.gwt.dev.jjs.ast.JBinaryOperation;
+import com.google.gwt.dev.jjs.ast.JBinaryOperator;
+import com.google.gwt.dev.jjs.ast.JExpression;
+import com.google.gwt.dev.jjs.ast.JMethod;
+import com.google.gwt.dev.jjs.ast.JMethodCall;
+import com.google.gwt.dev.jjs.ast.JModVisitor;
+import com.google.gwt.dev.jjs.ast.JPrimitiveType;
+import com.google.gwt.dev.jjs.ast.JProgram;
+import com.google.gwt.dev.jjs.ast.JReferenceType;
+import com.google.gwt.dev.jjs.ast.JType;
+
+/**
+ * Removes all assertion statements from the AST.
+ */
+public class AssertionNormalizer {
+
+  /**
+   * Normalizes all asserts.
+   */
+  private class AssertNormalizeVisitor extends JModVisitor {
+
+    public void endVisit(JAssertStatement x, Context ctx) {
+      JExpression lhs = x.getTestExpr();
+      String methodName = "Exceptions.throwAssertionError"
+          + getAssertMethodSuffix(x.getArg());
+      JMethod method = program.getIndexedMethod(methodName);
+      JMethodCall rhs = new JMethodCall(program, x.getSourceInfo(), null,
+          method);
+      if (x.getArg() != null) {
+        rhs.getArgs().add(x.getArg());
+      }
+      JBinaryOperation binOp = new JBinaryOperation(program, x.getSourceInfo(),
+          program.getTypePrimitiveBoolean(), JBinaryOperator.OR, lhs, rhs);
+      ctx.replaceMe(binOp.makeStatement());
+    }
+  }
+
+  public static void exec(JProgram program) {
+    new AssertionNormalizer(program).execImpl();
+  }
+
+  private static String getAssertMethodSuffix(JExpression arg) {
+    if (arg == null) {
+      return "";
+    }
+    JType argType = arg.getType();
+    if (argType instanceof JReferenceType) {
+      return "_Object";
+    }
+
+    assert (argType instanceof JPrimitiveType);
+    return "_" + argType.getName();
+  }
+
+  private final JProgram program;
+
+  public AssertionNormalizer(JProgram program) {
+    this.program = program;
+  }
+
+  private void execImpl() {
+    AssertNormalizeVisitor assertNormalizer = new AssertNormalizeVisitor();
+    assertNormalizer.accept(program);
+  }
+}
diff --git a/dev/core/src/com/google/gwt/dev/jjs/impl/AssertionRemover.java b/dev/core/src/com/google/gwt/dev/jjs/impl/AssertionRemover.java
index fd13b6d..685de4e 100644
--- a/dev/core/src/com/google/gwt/dev/jjs/impl/AssertionRemover.java
+++ b/dev/core/src/com/google/gwt/dev/jjs/impl/AssertionRemover.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2007 Google Inc.
+ * Copyright 2008 Google Inc.
  * 
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not
  * use this file except in compliance with the License. You may obtain a copy of
@@ -30,7 +30,7 @@
   /**
    * Removes all asserts.
    */
-  public class AssertVisitor extends JModVisitor {
+  private class AssertRemoveVisitor extends JModVisitor {
 
     public void endVisit(JAssertStatement x, Context ctx) {
       removeMe(x, ctx);
@@ -57,7 +57,7 @@
   }
 
   private void execImpl() {
-    AssertVisitor assertVisitor = new AssertVisitor();
-    assertVisitor.accept(program);
+    AssertRemoveVisitor assertRemover = new AssertRemoveVisitor();
+    assertRemover.accept(program);
   }
 }
diff --git a/dev/core/src/com/google/gwt/util/tools/ArgHandlerEnableAssertions.java b/dev/core/src/com/google/gwt/util/tools/ArgHandlerEnableAssertions.java
new file mode 100644
index 0000000..f37fa97
--- /dev/null
+++ b/dev/core/src/com/google/gwt/util/tools/ArgHandlerEnableAssertions.java
@@ -0,0 +1,46 @@
+/*
+ * Copyright 2008 Google Inc.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.google.gwt.util.tools;
+
+import com.google.gwt.dev.jjs.JJSOptions;
+
+/**
+ * Handles the -ea command line flag.
+ */
+public class ArgHandlerEnableAssertions extends ArgHandlerFlag {
+
+  private final JJSOptions optionsToModify;
+
+  public ArgHandlerEnableAssertions(JJSOptions optionsToModify) {
+    this.optionsToModify = optionsToModify;
+  }
+
+  @Override
+  public String getPurpose() {
+    return "Debugging: causes the compiled output to check assert statements.";
+  }
+
+  @Override
+  public String getTag() {
+    return "-ea";
+  }
+
+  @Override
+  public boolean setFlag() {
+    optionsToModify.setEnableAssertions(true);
+    return true;
+  }
+}
diff --git a/user/super/com/google/gwt/emul/java/lang/AssertionError.java b/user/super/com/google/gwt/emul/java/lang/AssertionError.java
index ada4174..bbd3d65 100644
--- a/user/super/com/google/gwt/emul/java/lang/AssertionError.java
+++ b/user/super/com/google/gwt/emul/java/lang/AssertionError.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2006 Google Inc.
+ * Copyright 2008 Google Inc.
  * 
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not
  * use this file except in compliance with the License. You may obtain a copy of
@@ -23,15 +23,6 @@
   public AssertionError() {
   }
 
-  private AssertionError(String message) {
-    super(message);
-  }
-
-  public AssertionError(Object message) {
-    super(String.valueOf(message), message instanceof Throwable
-      ? (Throwable) message : null);
-  }
-
   public AssertionError(boolean message) {
     this(String.valueOf(message));
   }
@@ -40,6 +31,14 @@
     this(String.valueOf(message));
   }
 
+  public AssertionError(double message) {
+    this(String.valueOf(message));
+  }
+
+  public AssertionError(float message) {
+    this(String.valueOf(message));
+  }
+
   public AssertionError(int message) {
     this(String.valueOf(message));
   }
@@ -48,11 +47,12 @@
     this(String.valueOf(message));
   }
 
-  public AssertionError(float message) {
-    this(String.valueOf(message));
+  public AssertionError(Object message) {
+    super(String.valueOf(message), message instanceof Throwable
+      ? (Throwable) message : null);
   }
 
-  public AssertionError(double message) {
-    this(String.valueOf(message));
+  private AssertionError(String message) {
+    super(message);
   }
 }
diff --git a/user/test/com/google/gwt/dev/jjs/test/CoverageTest.java b/user/test/com/google/gwt/dev/jjs/test/CoverageTest.java
index fa1fd27..e8ee773 100644
--- a/user/test/com/google/gwt/dev/jjs/test/CoverageTest.java
+++ b/user/test/com/google/gwt/dev/jjs/test/CoverageTest.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2007 Google Inc.
+ * Copyright 2008 Google Inc.
  * 
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not
  * use this file except in compliance with the License. You may obtain a copy of
@@ -54,7 +54,7 @@
           next.foo();
           CoverageTest.this.next.foo();
           CoverageTest.this.x = z;
-          CoverageTest.super.x = z; // inexpressible in Java without name mangling
+          CoverageTest.super.x = z;
         }
 
         public void foo() {
@@ -65,7 +65,7 @@
           next.foo();
           CoverageTest.this.next.foo();
           CoverageTest.this.x = z;
-          CoverageTest.super.x = z; // inexpressible in Java without name mangling
+          CoverageTest.super.x = z;
         }
       };
 
@@ -148,22 +148,85 @@
       ia[0] = i;
     }
 
-    /**
-     * TODO(later): implement asserts.
-     */
     private void testAssertStatement() {
-      // i = 1;
-      // try {
-      // assert i == 2;
-      // fail();
-      // } catch (AssertionError e) {
-      // }
-      // try {
-      // assert i == 3 : "foo";
-      // fail();
-      // } catch (AssertionError e) {
-      // assertEquals("foo", e.getMessage());
-      // }
+      // AssertStatement
+
+      // See if assertions are even enabled.
+      try {
+        assert false;
+        // Assertions are not on, early out.
+        return;
+      } catch (AssertionError e) {
+        // Assertions are on, run the test.
+      }
+
+      i = 1;
+      try {
+        assert i == 2;
+        fail();
+      } catch (AssertionError e) {
+      }
+
+      try {
+        assert i == 3 : true;
+        fail();
+      } catch (AssertionError e) {
+        assertEquals("true", e.getMessage());
+      }
+
+      try {
+        assert i == 3 : 'c';
+        fail();
+      } catch (AssertionError e) {
+        assertEquals("c", e.getMessage());
+      }
+
+      try {
+        assert i == 3 : 1.1;
+        fail();
+      } catch (AssertionError e) {
+        assertEquals("1.1", e.getMessage());
+      }
+
+      try {
+        assert i == 3 : 1.2f;
+        fail();
+      } catch (AssertionError e) {
+        assertEquals("1.2", e.getMessage());
+      }
+
+      try {
+        assert i == 3 : 5;
+        fail();
+      } catch (AssertionError e) {
+        assertEquals("5", e.getMessage());
+      }
+
+      try {
+        assert i == 3 : 6L;
+        fail();
+      } catch (AssertionError e) {
+        assertEquals("6", e.getMessage());
+      }
+
+      try {
+        assert i == 3 : "foo";
+        fail();
+      } catch (AssertionError e) {
+        assertEquals("foo", e.getMessage());
+      }
+
+      try {
+        assert i == 3 : new Object() {
+          @Override
+          public String toString() {
+            return "bar";
+          }
+        };
+        fail();
+      } catch (AssertionError e) {
+        assertEquals("bar", e.getMessage());
+      }
     }
 
     private void testAssignment() {
@@ -486,7 +549,8 @@
       assertEquals(21, i);
       i = Inner.this.i + Inner.this.j + Inner.this.x + Inner.this.y;
       assertEquals(30, i);
-      i = CoverageTest.this.i + CoverageTest.this.j + CoverageTest.this.x + CoverageTest.this.y;
+      i = CoverageTest.this.i + CoverageTest.this.j + CoverageTest.this.x
+          + CoverageTest.this.y;
       assertEquals(15, i);
       i = super.i + super.j + super.x + super.y;
       assertEquals(25, i);