diff --git a/runtime/lib/vmservice.cc b/runtime/lib/vmservice.cc
index 1f3afd079f5..df4486274c6 100644
--- a/runtime/lib/vmservice.cc
+++ b/runtime/lib/vmservice.cc
@@ -83,8 +83,8 @@ class RegisterRunningIsolatesVisitor : public IsolateVisitor {
     const Object& r =
         Object::Handle(DartEntry::InvokeFunction(register_function_, args));
     if (FLAG_trace_service) {
-      OS::Print("vm-service: Isolate %s %" Pd64 " registered.\n",
-                name.ToCString(), port_id);
+      OS::PrintErr("vm-service: Isolate %s %" Pd64 " registered.\n",
+                   name.ToCString(), port_id);
     }
     ASSERT(!r.IsError());
   }
@@ -135,7 +135,7 @@ DEFINE_NATIVE_ENTRY(VMService_SendObjectRootServiceMessage, 1) {
 
 DEFINE_NATIVE_ENTRY(VMService_OnStart, 0) {
   if (FLAG_trace_service) {
-    OS::Print("vm-service: Booting dart:vmservice library.\n");
+    OS::PrintErr("vm-service: Booting dart:vmservice library.\n");
   }
   // Boot the dart:vmservice library.
   ServiceIsolate::BootVmServiceLibrary();
@@ -146,7 +146,7 @@ DEFINE_NATIVE_ENTRY(VMService_OnStart, 0) {
   // Register running isolates with service.
   RegisterRunningIsolatesVisitor register_isolates(thread);
   if (FLAG_trace_service) {
-    OS::Print("vm-service: Registering running isolates.\n");
+    OS::PrintErr("vm-service: Registering running isolates.\n");
   }
   Isolate::VisitIsolates(&register_isolates);
 #endif
@@ -155,10 +155,10 @@ DEFINE_NATIVE_ENTRY(VMService_OnStart, 0) {
 
 DEFINE_NATIVE_ENTRY(VMService_OnExit, 0) {
   if (FLAG_trace_service) {
-    OS::Print("vm-service: processed exit message.\n");
+    OS::PrintErr("vm-service: processed exit message.\n");
     MessageHandler* message_handler = isolate->message_handler();
-    OS::Print("vm-service: live ports = %" Pd "\n",
-              message_handler->live_ports());
+    OS::PrintErr("vm-service: live ports = %" Pd "\n",
+                 message_handler->live_ports());
   }
   return Object::null();
 }
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index d97a4cfa154..34ebc67aaef 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -587,8 +587,8 @@ void IsolateMessageHandler::NotifyPauseOnStart() {
     ServiceEvent pause_event(I, ServiceEvent::kPauseStart);
     Service::HandleEvent(&pause_event);
   } else if (FLAG_trace_service) {
-    OS::Print("vm-service: Dropping event of type PauseStart (%s)\n",
-              I->name());
+    OS::PrintErr("vm-service: Dropping event of type PauseStart (%s)\n",
+                 I->name());
   }
 }
 
@@ -603,7 +603,8 @@ void IsolateMessageHandler::NotifyPauseOnExit() {
     ServiceEvent pause_event(I, ServiceEvent::kPauseExit);
     Service::HandleEvent(&pause_event);
   } else if (FLAG_trace_service) {
-    OS::Print("vm-service: Dropping event of type PauseExit (%s)\n", I->name());
+    OS::PrintErr("vm-service: Dropping event of type PauseExit (%s)\n",
+                 I->name());
   }
 }
 #endif  // !PRODUCT
@@ -2161,13 +2162,13 @@ RawObject* Isolate::InvokePendingServiceExtensionCalls() {
     arguments.SetAt(kPendingEntrySize, Bool::Get(FLAG_trace_service));
 
     if (FLAG_trace_service) {
-      OS::Print("[+%" Pd64 "ms] Isolate %s invoking _runExtension for %s\n",
-                Dart::UptimeMillis(), name(), method_name.ToCString());
+      OS::PrintErr("[+%" Pd64 "ms] Isolate %s invoking _runExtension for %s\n",
+                   Dart::UptimeMillis(), name(), method_name.ToCString());
     }
     result = DartEntry::InvokeFunction(run_extension, arguments);
     if (FLAG_trace_service) {
-      OS::Print("[+%" Pd64 "ms] Isolate %s : _runExtension complete for %s\n",
-                Dart::UptimeMillis(), name(), method_name.ToCString());
+      OS::PrintErr("[+%" Pd64 "ms] Isolate %s _runExtension complete for %s\n",
+                   Dart::UptimeMillis(), name(), method_name.ToCString());
     }
     // Propagate the error.
     if (result.IsError()) {
@@ -2203,8 +2204,9 @@ void Isolate::AppendServiceExtensionCall(const Instance& closure,
                                          const Instance& reply_port,
                                          const Instance& id) {
   if (FLAG_trace_service) {
-    OS::Print("[+%" Pd64 "ms] Isolate %s ENQUEUING request for extension %s\n",
-              Dart::UptimeMillis(), name(), method_name.ToCString());
+    OS::PrintErr("[+%" Pd64
+                 "ms] Isolate %s ENQUEUING request for extension %s\n",
+                 Dart::UptimeMillis(), name(), method_name.ToCString());
   }
   GrowableObjectArray& calls =
       GrowableObjectArray::Handle(pending_service_extension_calls());
diff --git a/runtime/vm/json_stream.cc b/runtime/vm/json_stream.cc
index 8700dc787a4..4c229c9f368 100644
--- a/runtime/vm/json_stream.cc
+++ b/runtime/vm/json_stream.cc
@@ -124,8 +124,8 @@ void JSONStream::Setup(Zone* zone,
     ASSERT(isolate != NULL);
     const char* isolate_name = isolate->name();
     setup_time_micros_ = OS::GetCurrentTimeMicros();
-    OS::Print("[+%" Pd64 "ms] Isolate %s processing service request %s\n",
-              Dart::UptimeMillis(), isolate_name, method_);
+    OS::PrintErr("[+%" Pd64 "ms] Isolate %s processing service request %s\n",
+                 Dart::UptimeMillis(), isolate_name, method_);
   }
   buffer_.Printf("{\"jsonrpc\":\"2.0\", \"result\":");
 }
@@ -282,15 +282,15 @@ void JSONStream::PostReply() {
     const char* isolate_name = isolate->name();
     int64_t total_time = OS::GetCurrentTimeMicros() - setup_time_micros_;
     if (result) {
-      OS::Print("[+%" Pd64
-                "ms] Isolate %s processed service request %s "
-                "(%" Pd64 "us)\n",
-                Dart::UptimeMillis(), isolate_name, method_, total_time);
+      OS::PrintErr("[+%" Pd64
+                   "ms] Isolate %s processed service request %s "
+                   "(%" Pd64 "us)\n",
+                   Dart::UptimeMillis(), isolate_name, method_, total_time);
     } else {
-      OS::Print("[+%" Pd64
-                "ms] Isolate %s processed service request %s "
-                "(%" Pd64 "us) FAILED\n",
-                Dart::UptimeMillis(), isolate_name, method_, total_time);
+      OS::PrintErr("[+%" Pd64
+                   "ms] Isolate %s processed service request %s "
+                   "(%" Pd64 "us) FAILED\n",
+                   Dart::UptimeMillis(), isolate_name, method_, total_time);
     }
   }
 }
diff --git a/runtime/vm/service.cc b/runtime/vm/service.cc
index 658dd69da54..b47a133c76a 100644
--- a/runtime/vm/service.cc
+++ b/runtime/vm/service.cc
@@ -130,7 +130,7 @@ static StreamInfo* streams_[] = {
 
 bool Service::ListenStream(const char* stream_id) {
   if (FLAG_trace_service) {
-    OS::Print("vm-service: starting stream '%s'\n", stream_id);
+    OS::PrintErr("vm-service: starting stream '%s'\n", stream_id);
   }
   intptr_t num_streams = sizeof(streams_) / sizeof(streams_[0]);
   for (intptr_t i = 0; i < num_streams; i++) {
@@ -149,7 +149,7 @@ bool Service::ListenStream(const char* stream_id) {
 
 void Service::CancelStream(const char* stream_id) {
   if (FLAG_trace_service) {
-    OS::Print("vm-service: stopping stream '%s'\n", stream_id);
+    OS::PrintErr("vm-service: stopping stream '%s'\n", stream_id);
   }
   intptr_t num_streams = sizeof(streams_) / sizeof(streams_[0]);
   for (intptr_t i = 0; i < num_streams; i++) {
@@ -912,7 +912,7 @@ void Service::SendEvent(const char* stream_id,
   ASSERT(!ServiceIsolate::IsServiceIsolateDescendant(isolate));
 
   if (FLAG_trace_service) {
-    OS::Print(
+    OS::PrintErr(
         "vm-service: Pushing ServiceEvent(isolate='%s', kind='%s',"
         " len=%" Pd ") to stream %s\n",
         isolate->name(), event_type, bytes_length, stream_id);
@@ -1097,7 +1097,7 @@ void Service::PostEvent(Isolate* isolate,
     if (isolate != NULL) {
       isolate_name = isolate->name();
     }
-    OS::Print(
+    OS::PrintErr(
         "vm-service: Pushing ServiceEvent(isolate='%s', kind='%s') "
         "to stream %s\n",
         isolate_name, kind, stream_id);
diff --git a/runtime/vm/service_isolate.cc b/runtime/vm/service_isolate.cc
index 1826f16fbe8..4aacb9189d1 100644
--- a/runtime/vm/service_isolate.cc
+++ b/runtime/vm/service_isolate.cc
@@ -199,8 +199,8 @@ bool ServiceIsolate::SendIsolateStartupMessage() {
   writer.WriteMessage(list);
   intptr_t len = writer.BytesWritten();
   if (FLAG_trace_service) {
-    OS::Print("vm-service: Isolate %s %" Pd64 " registered.\n",
-              name.ToCString(), Dart_GetMainPortId());
+    OS::PrintErr("vm-service: Isolate %s %" Pd64 " registered.\n",
+                 name.ToCString(), Dart_GetMainPortId());
   }
   return PortMap::PostMessage(
       new Message(port_, data, len, Message::kNormalPriority));
@@ -227,8 +227,8 @@ bool ServiceIsolate::SendIsolateShutdownMessage() {
   writer.WriteMessage(list);
   intptr_t len = writer.BytesWritten();
   if (FLAG_trace_service) {
-    OS::Print("vm-service: Isolate %s %" Pd64 " deregistered.\n",
-              name.ToCString(), Dart_GetMainPortId());
+    OS::PrintErr("vm-service: Isolate %s %" Pd64 " deregistered.\n",
+                 name.ToCString(), Dart_GetMainPortId());
   }
   return PortMap::PostMessage(
       new Message(port_, data, len, Message::kNormalPriority));
@@ -242,7 +242,7 @@ void ServiceIsolate::SendServiceExitMessage() {
     return;
   }
   if (FLAG_trace_service) {
-    OS::Print("vm-service: sending service exit message.\n");
+    OS::PrintErr("vm-service: sending service exit message.\n");
   }
   PortMap::PostMessage(new Message(port_, exit_message_, exit_message_length_,
                                    Message::kNormalPriority));
@@ -366,7 +366,7 @@ class RunServiceTask : public ThreadPool::Task {
  protected:
   static void ShutdownIsolate(uword parameter) {
     if (FLAG_trace_service) {
-      OS::Print("vm-service: ShutdownIsolate\n");
+      OS::PrintErr("vm-service: ShutdownIsolate\n");
     }
     Isolate* I = reinterpret_cast<Isolate*>(parameter);
     ASSERT(ServiceIsolate::IsServiceIsolate(I));
@@ -396,7 +396,7 @@ class RunServiceTask : public ThreadPool::Task {
     // Shut the isolate down.
     Dart::ShutdownIsolate(I);
     if (FLAG_trace_service) {
-      OS::Print("vm-service: Shutdown.\n");
+      OS::PrintErr("vm-service: Shutdown.\n");
     }
     ServiceIsolate::FinishedExiting();
   }
@@ -411,7 +411,7 @@ class RunServiceTask : public ThreadPool::Task {
         Library::Handle(Z, I->object_store()->root_library());
     if (root_library.IsNull()) {
       if (FLAG_trace_service) {
-        OS::Print("vm-service: Embedder did not install a script.");
+        OS::PrintErr("vm-service: Embedder did not install a script.");
       }
       // Service isolate is not supported by embedder.
       return false;
@@ -424,7 +424,7 @@ class RunServiceTask : public ThreadPool::Task {
     if (entry.IsNull()) {
       // Service isolate is not supported by embedder.
       if (FLAG_trace_service) {
-        OS::Print("vm-service: Embedder did not provide a main function.");
+        OS::PrintErr("vm-service: Embedder did not provide a main function.");
       }
       return false;
     }
@@ -436,8 +436,8 @@ class RunServiceTask : public ThreadPool::Task {
       // Service isolate did not initialize properly.
       if (FLAG_trace_service) {
         const Error& error = Error::Cast(result);
-        OS::Print("vm-service: Calling main resulted in an error: %s",
-                  error.ToErrorCString());
+        OS::PrintErr("vm-service: Calling main resulted in an error: %s",
+                     error.ToErrorCString());
       }
       if (result.IsUnwindError()) {
         return true;
diff --git a/runtime/vm/thread.cc b/runtime/vm/thread.cc
index 715d3b8f82e..4273fbb0d7c 100644
--- a/runtime/vm/thread.cc
+++ b/runtime/vm/thread.cc
@@ -510,8 +510,8 @@ void Thread::DeferOOBMessageInterrupts() {
     }
   }
   if (FLAG_trace_service && FLAG_trace_service_verbose) {
-    OS::Print("[+%" Pd64 "ms] Isolate %s deferring OOB interrupts\n",
-              Dart::UptimeMillis(), isolate()->name());
+    OS::PrintErr("[+%" Pd64 "ms] Isolate %s deferring OOB interrupts\n",
+                 Dart::UptimeMillis(), isolate()->name());
   }
 }
 
@@ -532,8 +532,8 @@ void Thread::RestoreOOBMessageInterrupts() {
     deferred_interrupts_ = 0;
   }
   if (FLAG_trace_service && FLAG_trace_service_verbose) {
-    OS::Print("[+%" Pd64 "ms] Isolate %s restoring OOB interrupts\n",
-              Dart::UptimeMillis(), isolate()->name());
+    OS::PrintErr("[+%" Pd64 "ms] Isolate %s restoring OOB interrupts\n",
+                 Dart::UptimeMillis(), isolate()->name());
   }
 }