diff --git a/sdk/lib/_internal/lib/isolate_helper.dart b/sdk/lib/_internal/lib/isolate_helper.dart
index 05208648a9a..cd3ee4ad56d 100644
--- a/sdk/lib/_internal/lib/isolate_helper.dart
+++ b/sdk/lib/_internal/lib/isolate_helper.dart
@@ -22,8 +22,6 @@ import 'dart:_foreign_helper' show DART_CLOSURE_TO_JS,
                                    IsolateContext;
 import 'dart:_interceptors' show JSExtendableArray;
 
-ReceivePort controlPort;
-
 /**
  * Called by the compiler to support switching
  * between isolates when we get a callback from the DOM.
@@ -236,6 +234,39 @@ class _IsolateContext implements IsolateContext {
   // native object containing all globals of an isolate.
   final isolateStatics = JS_CREATE_ISOLATE();
 
+  final RawReceivePortImpl controlPort = new RawReceivePortImpl._controlPort();
+
+  final Capability pauseCapability = new Capability();
+
+  // TODO(lrn): Store these in single "pausestate" object, so they don't take
+  // up as much room when not pausing.
+  bool isPaused = false;
+  List<_IsolateEvent> delayedEvents = [];
+  Set<Capability> pauseTokens = new Set();
+
+  _IsolateContext() {
+    this.registerWeak(controlPort._id, controlPort);
+  }
+
+  void addPause(Capability authentification, Capability resume) {
+    if (pauseCapability != authentification) return;
+    if (pauseTokens.add(resume) && !isPaused) {
+      isPaused = true;
+    }
+  }
+
+  void removePause(Capability resume) {
+    if (!isPaused) return;
+    pauseTokens.remove(resume);
+    if (pauseTokens.isEmpty) {
+      while(delayedEvents.isNotEmpty) {
+        _IsolateEvent event = delayedEvents.removeLast();
+        _globalState.topEventLoop.prequeue(event);
+      }
+      isPaused = false;
+    }
+  }
+
   /**
    * Run [code] in the context of the isolate represented by [this].
    */
@@ -257,15 +288,32 @@ class _IsolateContext implements IsolateContext {
     JS_SET_CURRENT_ISOLATE(isolateStatics);
   }
 
+  void handleControlMessage(message) {
+    switch (message[0]) {
+      case "pause":
+        addPause(message[1], message[2]);
+        break;
+      case "resume":
+        removePause(message[1]);
+        break;
+      default:
+        print("UNKOWN MESSAGE: $message");
+    }
+  }
+
   /** Looks up a port registered for this isolate. */
   RawReceivePortImpl lookup(int portId) => ports[portId];
 
-  /** Registers a port on this isolate. */
-  void register(int portId, RawReceivePortImpl port)  {
+  void _addRegistration(int portId, RawReceivePortImpl port) {
     if (ports.containsKey(portId)) {
       throw new Exception("Registry: ports must be registered only once.");
     }
     ports[portId] = port;
+  }
+
+  /** Registers a port on this isolate. */
+  void register(int portId, RawReceivePortImpl port)  {
+    _addRegistration(portId, port);
     _updateGlobalState();
   }
 
@@ -276,8 +324,7 @@ class _IsolateContext implements IsolateContext {
    */
   void registerWeak(int portId, RawReceivePortImpl port)  {
     weakPorts.add(portId);
-    // 'register' updates the global state.
-    register(portId, port);
+    _addRegistration(portId, port);
   }
 
   _updateGlobalState() {
@@ -291,6 +338,7 @@ class _IsolateContext implements IsolateContext {
   /** Unregister a port on this isolate. */
   void unregister(int portId) {
     ports.remove(portId);
+    weakPorts.remove(portId);
     _updateGlobalState();
   }
 }
@@ -306,6 +354,10 @@ class _EventLoop {
     events.addLast(new _IsolateEvent(isolate, fn, msg));
   }
 
+  void prequeue(_IsolateEvent event) {
+    events.addFirst(event);
+  }
+
   _IsolateEvent dequeue() {
     if (events.isEmpty) return null;
     return events.removeFirst();
@@ -383,6 +435,10 @@ class _IsolateEvent {
   _IsolateEvent(this.isolate, this.fn, this.message);
 
   void process() {
+    if (isolate.isPaused) {
+      isolate.delayedEvents.add(this);
+      return;
+    }
     isolate.eval(fn);
   }
 }
@@ -582,7 +638,7 @@ class IsolateNatives {
     return JS("", "new #()", ctor);
   }
 
-  static Future<SendPort> spawnFunction(void topLevelFunction(message),
+  static Future<List> spawnFunction(void topLevelFunction(message),
                                         message) {
     final name = _getJSFunctionName(topLevelFunction);
     if (name == null) {
@@ -592,25 +648,25 @@ class IsolateNatives {
     return spawn(name, null, null, message, false, false);
   }
 
-  static Future<SendPort> spawnUri(Uri uri, List<String> args, message) {
+  static Future<List> spawnUri(Uri uri, List<String> args, message) {
     return spawn(null, uri.toString(), args, message, false, true);
   }
 
   // TODO(sigmund): clean up above, after we make the new API the default:
 
   /// If [uri] is `null` it is replaced with the current script.
-  static Future<SendPort> spawn(String functionName, String uri,
-                                List<String> args, message,
-                                bool isLight, bool isSpawnUri) {
+  static Future<List> spawn(String functionName, String uri,
+                            List<String> args, message,
+                            bool isLight, bool isSpawnUri) {
     // Assume that the compiled version of the Dart file lives just next to the
     // dart file.
     // TODO(floitsch): support precompiled version of dart2js output.
     if (uri != null && uri.endsWith(".dart")) uri += ".js";
 
     ReceivePort port = new ReceivePort();
-    Future<SendPort> result = port.first.then((msg) {
+    Future<List> result = port.first.then((msg) {
       assert(msg[0] == _SPAWNED_SIGNAL);
-      return msg[1];
+      return msg;
     });
 
     SendPort signalReply = port.sendPort;
@@ -666,8 +722,9 @@ class IsolateNatives {
     _IsolateContext context = JS_CURRENT_ISOLATE_CONTEXT();
     Primitives.initializeStatics(context.id);
     // The isolate's port does not keep the isolate open.
-    controlPort = new ReceivePortImpl.weak();
-    replyTo.send([_SPAWNED_SIGNAL, controlPort.sendPort]);
+    replyTo.send([_SPAWNED_SIGNAL,
+                  context.controlPort.sendPort,
+                  context.pauseCapability]);
     if (!isSpawnUri) {
       topLevel(message);
     } else if (topLevel is _MainFunctionArgsMessage) {
@@ -763,6 +820,10 @@ class _NativeJsSendPort extends _BaseSendPort implements SendPort {
     if (shouldSerialize) {
       msg = _serializeMessage(msg);
     }
+    if (isolate.controlPort == _receivePort) {
+      isolate.handleControlMessage(msg);
+      return;
+    }
     _globalState.topEventLoop.enqueue(isolate, () {
       if (!_receivePort._isClosed) {
         if (shouldSerialize) {
@@ -823,18 +884,23 @@ class _WorkerSendPort extends _BaseSendPort implements SendPort {
 class RawReceivePortImpl implements RawReceivePort {
   static int _nextFreeId = 1;
 
-  final int _id = _nextFreeId++;
+  final int _id;
   Function _handler;
   bool _isClosed = false;
 
-  RawReceivePortImpl(this._handler) {
+  RawReceivePortImpl(this._handler) : _id = _nextFreeId++ {
     _globalState.currentContext.register(_id, this);
   }
 
-  RawReceivePortImpl.weak(this._handler) {
+  RawReceivePortImpl.weak(this._handler) : _id = _nextFreeId++ {
     _globalState.currentContext.registerWeak(_id, this);
   }
 
+  // Creates the control port of an isolate.
+  // This is created before the isolate context object itself,
+  // so it cannot access the static _nextFreeId field.
+  RawReceivePortImpl._controlPort() : _handler = null, _id = 0;
+
   void set handler(Function newHandler) {
     _handler = newHandler;
   }
diff --git a/sdk/lib/_internal/lib/isolate_patch.dart b/sdk/lib/_internal/lib/isolate_patch.dart
index 09b79553abb..9d931a95c99 100644
--- a/sdk/lib/_internal/lib/isolate_patch.dart
+++ b/sdk/lib/_internal/lib/isolate_patch.dart
@@ -15,7 +15,7 @@ patch class Isolate {
   patch static Future<Isolate> spawn(void entryPoint(message), var message) {
     try {
       return IsolateNatives.spawnFunction(entryPoint, message)
-          .then((controlPort) => new Isolate._fromControlPort(controlPort));
+          .then((msg) => new Isolate._fromControlPort(msg[1], msg[2]));
     } catch (e, st) {
       return new Future<Isolate>.error(e, st);
     }
@@ -34,7 +34,7 @@ patch class Isolate {
         throw new ArgumentError("Args must be a list of Strings $args");
       }
       return IsolateNatives.spawnUri(uri, args, message)
-          .then((controlPort) => new Isolate._fromControlPort(controlPort));
+          .then((msg) => new Isolate._fromControlPort(msg[1], msg[2]));
     } catch (e, st) {
       return new Future<Isolate>.error(e, st);
     }
diff --git a/tests/isolate/isolate.status b/tests/isolate/isolate.status
index a753ec2dbc5..b2517d12f4b 100644
--- a/tests/isolate/isolate.status
+++ b/tests/isolate/isolate.status
@@ -11,17 +11,17 @@ serialization_test: SkipByDesign # Tests dart2js-specific serialization code
 isolate_throws_test/01: Skip # Issue 12587
 compile_time_error_test/01: Skip # Issue 12587
 capability_test: Fail  # Not implemented yet
-pause_test: Fail
+pause_test: Fail       # Not implemented yet
 
 [ $compiler == dart2js && $jscl ]
 browser/*: SkipByDesign  # Browser specific tests
+pause_test: Fail  # non-zero timer not supported.
 
 [ $compiler == dart2js && $runtime == drt ]
 isolate_stress_test: Pass, Crash # Issue 14438
 
 [ $compiler == dart2js ]
 serialization_test: RuntimeError # Issue 1882, tries to access class TestingOnly declared in isolate_patch.dart
-pause_test: Fail
 
 [ $compiler == dart2js && $runtime == ie9 ]
 browser/typed_data_message_test: Fail # Issue 12624
diff --git a/tests/isolate/pause_test.dart b/tests/isolate/pause_test.dart
index 71691adfc8c..22a4fce6018 100644
--- a/tests/isolate/pause_test.dart
+++ b/tests/isolate/pause_test.dart
@@ -24,10 +24,10 @@ main(){
   reply.handler = completer.complete;
   Isolate.spawn(isomain1, reply.sendPort).then((Isolate iso) {
     isolate = iso;
-    resume = isolate.pause();
     return completer.future;
   }).then((echoPort) {
     // Isolate has been created, and first response has been returned.
+    resume = isolate.pause();
     echoPort.send(24);
     reply.handler = (v) {
       throw "RESPONSE WHILE PAUSED?!?";