diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index 33cce48323..f6b09c84d9 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Don't quote hash keys in Hash#to_json if they're valid JavaScript identifiers.  Disable this with ActiveSupport::JSON.unquote_hash_key_identifiers = false if you need strict JSON compliance. [Sam Stephenson]
+
 * Lazily load the Unicode Database in the UTF-8 Handler [Rick Olson]
 
 * Update dependencies to delete partially loaded constants. [Nicholas Seckar]
diff --git a/activesupport/lib/active_support/json.rb b/activesupport/lib/active_support/json.rb
index 7d5304ddd4..d1203bd21b 100644
--- a/activesupport/lib/active_support/json.rb
+++ b/activesupport/lib/active_support/json.rb
@@ -4,14 +4,20 @@ module ActiveSupport
   module JSON #:nodoc:
     class CircularReferenceError < StandardError #:nodoc:
     end
-    # returns the literal string as its JSON encoded form.  Useful for passing javascript variables into functions.
-    #
-    # page.call 'Element.show', ActiveSupport::JSON::Variable.new("$$(#items li)")
+    
+    # A string that returns itself as as its JSON-encoded form.
     class Variable < String #:nodoc:
       def to_json
         self
       end
     end
+    
+    # When +true+, Hash#to_json will omit quoting string or symbol keys
+    # if the keys are valid JavaScript identifiers.  Note that this is
+    # technically improper JSON (all object keys must be quoted), so if
+    # you need strict JSON compliance, set this option to +false+.
+    mattr_accessor :unquote_hash_key_identifiers
+    @@unquote_hash_key_identifiers = true
 
     class << self
       REFERENCE_STACK_VARIABLE = :json_reference_stack
@@ -22,6 +28,11 @@ def encode(value)
         end
       end
       
+      def can_unquote_identifier?(key)
+        return false unless unquote_hash_key_identifiers
+        key.to_s =~ /^[[:alpha:]_$][[:alnum:]_$]*$/
+      end
+      
       protected
         def raise_on_circular_reference(value)
           stack = Thread.current[REFERENCE_STACK_VARIABLE] ||= []
diff --git a/activesupport/lib/active_support/json/encoders/core.rb b/activesupport/lib/active_support/json/encoders/core.rb
index d8571be9c8..f6cdfbcde5 100644
--- a/activesupport/lib/active_support/json/encoders/core.rb
+++ b/activesupport/lib/active_support/json/encoders/core.rb
@@ -51,8 +51,10 @@ module Encoders #:nodoc:
       
       define_encoder Hash do |hash|
         returning result = '{' do
-          result << hash.map do |pair|
-            pair.map { |value| value.to_json } * ': '
+          result << hash.map do |key, value|
+            key = ActiveSupport::JSON::Variable.new(key.to_s) if 
+              ActiveSupport::JSON.can_unquote_identifier?(key)
+            "#{key.to_json}: #{value.to_json}"
           end * ', '
           result << '}'
         end
diff --git a/activesupport/test/json.rb b/activesupport/test/json.rb
index 33c5a64ba5..0274dd073a 100644
--- a/activesupport/test/json.rb
+++ b/activesupport/test/json.rb
@@ -36,6 +36,14 @@ class TestJSONEmitters < Test::Unit::TestCase
       end
     end
   end
+
+  def setup
+    unquote(false)
+  end
+  
+  def teardown
+    unquote(true)
+  end
   
   def test_hash_encoding
     assert_equal %({\"a\": \"b\"}), { :a => :b }.to_json
@@ -60,4 +68,20 @@ def test_exception_raised_when_encoding_circular_reference
     a << a
     assert_raises(ActiveSupport::JSON::CircularReferenceError) { a.to_json }
   end
+  
+  def test_unquote_hash_key_identifiers
+    values = {0 => 0, 1 => 1, :_ => :_, "$" => "$", "a" => "a", :A => :A, :A0 => :A0, "A0B" => "A0B"}    
+    assert_equal %({"a": "a", 0: 0, "_": "_", 1: 1, "$": "$", "A": "A", "A0B": "A0B", "A0": "A0"}), values.to_json
+    unquote(true) { assert_equal %({a: "a", 0: 0, _: "_", 1: 1, $: "$", A: "A", A0B: "A0B", A0: "A0"}), values.to_json }
+  end
+  
+  protected
+    def unquote(value)
+      previous_value = ActiveSupport::JSON.unquote_hash_key_identifiers
+      ActiveSupport::JSON.unquote_hash_key_identifiers = value
+      yield if block_given?
+    ensure
+      ActiveSupport::JSON.unquote_hash_key_identifiers = previous_value if block_given?
+    end
+    
 end