diff --git a/grunt/tasks/version-check.js b/grunt/tasks/version-check.js
index b874f5a0d9da7..08839a47c9976 100644
--- a/grunt/tasks/version-check.js
+++ b/grunt/tasks/version-check.js
@@ -6,7 +6,7 @@ var grunt = require('grunt');
 // Check that the version we're exporting is the same one we expect in the
 // package. This is not an ideal way to do this, but makes sure that we keep
 // them in sync.
-var reactVersionExp = /\bREACT_VERSION\s*=\s*['"]([^'"]+)['"];/;
+var reactVersionExp = /\bReact\.version\s*=\s*['"]([^'"]+)['"];/;
 
 module.exports = function() {
   var reactVersion = reactVersionExp.exec(
diff --git a/src/browser/ui/React.js b/src/browser/ui/React.js
index ee0183206dcdf..ccead4fee025c 100644
--- a/src/browser/ui/React.js
+++ b/src/browser/ui/React.js
@@ -13,30 +13,6 @@
 
 'use strict';
 
-var REACT_VERSION = '0.14.0-alpha';
-
-var ExecutionEnvironment = require('ExecutionEnvironment');
-var warning = require('warning');
-
-if (__DEV__) {
-  // before performing any initialization of React, check that
-  // only one instance is in use on the current page.
-  //
-  // Using multiple instances cause a variety of problems if elements
-  // from different versions are mixed on the same page.
-  //
-  // See issue #2402
-  if (ExecutionEnvironment.canUseDOM) {
-    warning(
-      typeof window.__REACT_VERSION__ === 'undefined',
-      'Multiple instances of React have been initialized on the same page. ' +
-      'Currently initializing React v' + REACT_VERSION + ' but another instance of React v' +
-      window.__REACT_VERSION__ + ' was already initialized'
-    );
-    window.__REACT_VERSION__ = REACT_VERSION;
-  }
-}
-
 var ReactChildren = require('ReactChildren');
 var ReactComponent = require('ReactComponent');
 var ReactClass = require('ReactClass');
@@ -57,6 +33,7 @@ var ReactServerRendering = require('ReactServerRendering');
 var assign = require('Object.assign');
 var findDOMNode = require('findDOMNode');
 var onlyChild = require('onlyChild');
+var warning = require('warning');
 
 ReactDefaultInjection.inject();
 
@@ -73,7 +50,6 @@ if (__DEV__) {
 var render = ReactPerf.measure('React', 'render', ReactMount.render);
 
 var React = {
-  version: REACT_VERSION,
   Children: {
     map: ReactChildren.map,
     forEach: ReactChildren.forEach,
@@ -120,6 +96,7 @@ if (
 }
 
 if (__DEV__) {
+  var ExecutionEnvironment = require('ExecutionEnvironment');
   if (ExecutionEnvironment.canUseDOM && window.top === window.self) {
 
     // If we're in Chrome, look for the devtools marker and provide a download
@@ -175,4 +152,6 @@ if (__DEV__) {
   }
 }
 
+React.version = '0.14.0-alpha';
+
 module.exports = React;