diff --git a/actionpack/CHANGELOG b/actionpack/CHANGELOG
index 967bd76025d03..562b1dba3dd3c 100644
--- a/actionpack/CHANGELOG
+++ b/actionpack/CHANGELOG
@@ -1,10 +1,7 @@
-*Rails 3.0.0 [Release Candidate] (unreleased)*
-
-* Add support for multi-subdomain session by setting cookie host in session cookie so you can share session between www.example.com, example.com and user.example.com. #4818 [Guillermo Álvarez]
+Rails 3.0.0 [Release Candidate] (unreleased)*
 
 * Removed textilize, textilize_without_paragraph and markdown helpers. [Santiago Pastorino]
 
-
 *Rails 3.0.0 [beta 4] (June 8th, 2010)*
 
 * Remove middleware laziness [José Valim]
diff --git a/actionpack/lib/action_dispatch/middleware/session/abstract_store.rb b/actionpack/lib/action_dispatch/middleware/session/abstract_store.rb
index 040a83f7a6f8e..3e8d64b0c67c0 100644
--- a/actionpack/lib/action_dispatch/middleware/session/abstract_store.rb
+++ b/actionpack/lib/action_dispatch/middleware/session/abstract_store.rb
@@ -121,12 +121,7 @@ def call(env)
           unless options[:expire_after].nil?
             cookie[:expires] = Time.now + options.delete(:expire_after)
           end
-          
-          if options[:domain] == :all
-            top_level_domain = env["HTTP_HOST"].split('.')[-2..-1].join('.')
-            options[:domain] = ".#{top_level_domain}"
-          end
-          
+
           request = ActionDispatch::Request.new(env)
           set_cookie(request, cookie.merge!(options))
         end
diff --git a/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb b/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
index 0fc63d026fa61..92a86ee229635 100644
--- a/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
+++ b/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
@@ -34,14 +34,6 @@ module Session
     #   integrity defaults to 'SHA1' but may be any digest provided by OpenSSL,
     #   such as 'MD5', 'RIPEMD160', 'SHA256', etc.
     #
-    # * <tt>:domain</tt>: Restrict the session cookie to certain domain level.
-    #   If you use a schema like www.example.com and wants to share session 
-    #   with user.example.com set <tt>:domain</tt> to <tt>:all</tt>
-    #     
-    #     :domain => nil  # Does not sets cookie domain. (default)
-    #     :domain => :all # Allow the cookie for the top most level
-    #                       domain and subdomains.
-    #
     # To generate a secret key for an existing application, run
     # "rake secret" and set the key in config/environment.rb.
     #
diff --git a/actionpack/test/dispatch/session/cookie_store_test.rb b/actionpack/test/dispatch/session/cookie_store_test.rb
index b542824789e4b..21d11ff31c6f9 100644
--- a/actionpack/test/dispatch/session/cookie_store_test.rb
+++ b/actionpack/test/dispatch/session/cookie_store_test.rb
@@ -185,35 +185,6 @@ def test_session_store_with_expire_after
     end
   end
 
-  def test_session_store_with_explicit_domain
-    with_test_route_set(:domain => "example.es") do
-      get '/set_session_value'
-      assert_match /domain=example\.es/, headers['Set-Cookie']
-      headers['Set-Cookie']
-    end
-  end
-  
-  def test_session_store_without_domain 
-    with_test_route_set do
-      get '/set_session_value'
-      assert_no_match /domain\=/, headers['Set-Cookie']
-    end
-  end
-  
-  def test_session_store_with_nil_domain
-    with_test_route_set(:domain => nil) do
-      get '/set_session_value'
-      assert_no_match /domain\=/, headers['Set-Cookie']
-    end
-  end
-  
-  def test_session_store_with_all_domains
-    with_test_route_set(:domain => :all) do
-      get '/set_session_value'
-      assert_match /domain=\.example\.com/, headers['Set-Cookie']
-    end
-  end
-  
   private
 
     # Overwrite get to send SessionSecret in env hash