diff --git a/src/browser/server/ReactServerRendering.js b/src/browser/server/ReactServerRendering.js
index d29989e0cb710..fb5c45c37bd6f 100644
--- a/src/browser/server/ReactServerRendering.js
+++ b/src/browser/server/ReactServerRendering.js
@@ -40,7 +40,7 @@ function renderToString(element, context) {
 
     return transaction.perform(function() {
       var componentInstance = instantiateReactComponent(element, null);
-      var markup = componentInstance.mountComponent(id, transaction, 0, context);
+      var markup = componentInstance.mountComponent(id, transaction, context);
       return ReactMarkupChecksum.addChecksumToMarkup(markup);
     }, null);
   } finally {
@@ -68,7 +68,7 @@ function renderToStaticMarkup(element, context) {
 
     return transaction.perform(function() {
       var componentInstance = instantiateReactComponent(element, null);
-      return componentInstance.mountComponent(id, transaction, 0, context);
+      return componentInstance.mountComponent(id, transaction, context);
     }, null);
   } finally {
     ReactServerRenderingTransaction.release(transaction);
diff --git a/src/browser/ui/ReactDOMComponent.js b/src/browser/ui/ReactDOMComponent.js
index 5216a530e2d2f..42a044d15d10a 100644
--- a/src/browser/ui/ReactDOMComponent.js
+++ b/src/browser/ui/ReactDOMComponent.js
@@ -168,15 +168,13 @@ ReactDOMComponent.Mixin = {
    * @internal
    * @param {string} rootID The root DOM ID for this node.
    * @param {ReactReconcileTransaction|ReactServerRenderingTransaction} transaction
-   * @param {number} mountDepth number of components in the owner hierarchy
    * @return {string} The computed markup.
    */
-  mountComponent: function(rootID, transaction, mountDepth, context) {
+  mountComponent: function(rootID, transaction, context) {
     ReactComponent.Mixin.mountComponent.call(
       this,
       rootID,
       transaction,
-      mountDepth,
       context
     );
     this._rootNodeID = rootID;
diff --git a/src/browser/ui/ReactDOMTextComponent.js b/src/browser/ui/ReactDOMTextComponent.js
index 54e5c7acf2e9e..e12ee2753a950 100644
--- a/src/browser/ui/ReactDOMTextComponent.js
+++ b/src/browser/ui/ReactDOMTextComponent.js
@@ -62,11 +62,10 @@ assign(ReactDOMTextComponent.prototype, {
    *
    * @param {string} rootID DOM ID of the root node.
    * @param {ReactReconcileTransaction|ReactServerRenderingTransaction} transaction
-   * @param {number} mountDepth number of components in the owner hierarchy
    * @return {string} Markup for this text node.
    * @internal
    */
-  mountComponent: function(rootID, transaction, mountDepth, context) {
+  mountComponent: function(rootID, transaction, context) {
     this._rootNodeID = rootID;
     var escapedText = escapeTextForBrowser(this._stringText);
 
diff --git a/src/browser/ui/ReactMount.js b/src/browser/ui/ReactMount.js
index 90a874622d748..218a020667d5c 100644
--- a/src/browser/ui/ReactMount.js
+++ b/src/browser/ui/ReactMount.js
@@ -225,7 +225,8 @@ function mountComponentIntoNode(
     container,
     transaction,
     shouldReuseMarkup) {
-  var markup = this.mountComponent(rootID, transaction, 0, emptyObject);
+  var markup = this.mountComponent(rootID, transaction, emptyObject);
+  this._isTopLevel = true;
   ReactMount._mountImageIntoNode(markup, container, shouldReuseMarkup);
 }
 
diff --git a/src/browser/ui/__tests__/ReactDOMComponent-test.js b/src/browser/ui/__tests__/ReactDOMComponent-test.js
index 5427b832ba327..7bb8e24650216 100644
--- a/src/browser/ui/__tests__/ReactDOMComponent-test.js
+++ b/src/browser/ui/__tests__/ReactDOMComponent-test.js
@@ -328,7 +328,7 @@ describe('ReactDOMComponent', function() {
           _owner: null,
           _context: null
         });
-        return stubComponent.mountComponent('test', transaction, 0, {});
+        return stubComponent.mountComponent('test', transaction, {});
       };
     });
 
diff --git a/src/browser/ui/dom/__tests__/Danger-test.js b/src/browser/ui/dom/__tests__/Danger-test.js
index 1e2e6f02d338e..69f71c4655e80 100644
--- a/src/browser/ui/dom/__tests__/Danger-test.js
+++ b/src/browser/ui/dom/__tests__/Danger-test.js
@@ -32,7 +32,7 @@ describe('Danger', function() {
     it('should render markup', function() {
       var markup = instantiateReactComponent(
         <div />
-      ).mountComponent('.rX', transaction, 0, {});
+      ).mountComponent('.rX', transaction, {});
       var output = Danger.dangerouslyRenderMarkup([markup])[0];
 
       expect(output.nodeName).toBe('DIV');
@@ -44,7 +44,7 @@ describe('Danger', function() {
       ).mountComponent(
         '.rX',
         transaction,
-        0, {}
+        {}
       );
       var output = Danger.dangerouslyRenderMarkup([markup])[0];
 
@@ -55,7 +55,7 @@ describe('Danger', function() {
     it('should render wrapped markup', function() {
       var markup = instantiateReactComponent(
         <th />
-      ).mountComponent('.rX', transaction, 0, {});
+      ).mountComponent('.rX', transaction, {});
       var output = Danger.dangerouslyRenderMarkup([markup])[0];
 
       expect(output.nodeName).toBe('TH');
diff --git a/src/core/ReactComponent.js b/src/core/ReactComponent.js
index f9361bac20350..694d9578dd171 100644
--- a/src/core/ReactComponent.js
+++ b/src/core/ReactComponent.js
@@ -90,7 +90,6 @@ var ReactComponent = {
       // to track updates.
       this._currentElement = element;
       this._mountIndex = 0;
-      this._mountDepth = 0;
     },
 
     /**
@@ -103,17 +102,15 @@ var ReactComponent = {
      *
      * @param {string} rootID DOM ID of the root node.
      * @param {ReactReconcileTransaction|ReactServerRenderingTransaction} transaction
-     * @param {number} mountDepth number of components in the owner hierarchy.
      * @return {?string} Rendered markup to be inserted into the DOM.
      * @internal
      */
-    mountComponent: function(rootID, transaction, mountDepth, context) {
+    mountComponent: function(rootID, transaction, context) {
       var ref = this._currentElement.ref;
       if (ref != null) {
         var owner = this._currentElement._owner;
         attachRef(ref, this, owner);
       }
-      this._mountDepth = mountDepth;
       // Effectively: return '';
     },
 
diff --git a/src/core/ReactCompositeComponent.js b/src/core/ReactCompositeComponent.js
index bb43da310f1f5..192de12e4eb87 100644
--- a/src/core/ReactCompositeComponent.js
+++ b/src/core/ReactCompositeComponent.js
@@ -141,6 +141,7 @@ var ReactCompositeComponentMixin = assign({},
 
     this._context = null;
     this._mountOrder = 0;
+    this._isTopLevel = false;
 
     // See ReactUpdates.
     this._pendingCallbacks = null;
@@ -161,17 +162,15 @@ var ReactCompositeComponentMixin = assign({},
    *
    * @param {string} rootID DOM ID of the root node.
    * @param {ReactReconcileTransaction|ReactServerRenderingTransaction} transaction
-   * @param {number} mountDepth number of components in the owner hierarchy
    * @return {?string} Rendered markup to be inserted into the DOM.
    * @final
    * @internal
    */
-  mountComponent: function(rootID, transaction, mountDepth, context) {
+  mountComponent: function(rootID, transaction, context) {
     ReactComponent.Mixin.mountComponent.call(
       this,
       rootID,
       transaction,
-      mountDepth,
       context
     );
 
@@ -233,7 +232,6 @@ var ReactCompositeComponentMixin = assign({},
     var markup = this._renderedComponent.mountComponent(
       rootID,
       transaction,
-      mountDepth + 1,
       this._processChildContext(context)
     );
     if (inst.componentDidMount) {
@@ -313,7 +311,7 @@ var ReactCompositeComponentMixin = assign({},
    */
   replaceProps: function(props, callback) {
     invariant(
-      this._mountDepth === 0,
+      this._isTopLevel,
       'replaceProps(...): You called `setProps` or `replaceProps` on a ' +
       'component with a parent. This is an anti-pattern since props will ' +
       'get reactively updated when rendered. Instead, change the owner\'s ' +
@@ -781,7 +779,6 @@ var ReactCompositeComponentMixin = assign({},
       var nextMarkup = this._renderedComponent.mountComponent(
         thisID,
         transaction,
-        this._mountDepth + 1,
         context
       );
       ReactComponentEnvironment.replaceNodeWithMarkupByID(
@@ -890,17 +887,15 @@ var ShallowMixin = assign({},
    *
    * @param {string} rootID DOM ID of the root node.
    * @param {ReactReconcileTransaction|ReactServerRenderingTransaction} transaction
-   * @param {number} mountDepth number of components in the owner hierarchy
    * @return {ReactElement} Shallow rendering of the component.
    * @final
    * @internal
    */
-  mountComponent: function(rootID, transaction, mountDepth, context) {
+  mountComponent: function(rootID, transaction, context) {
     ReactComponent.Mixin.mountComponent.call(
       this,
       rootID,
       transaction,
-      mountDepth,
       context
     );
 
diff --git a/src/core/ReactMultiChild.js b/src/core/ReactMultiChild.js
index a6314fa87128c..15cf15b73fefe 100644
--- a/src/core/ReactMultiChild.js
+++ b/src/core/ReactMultiChild.js
@@ -195,7 +195,6 @@ var ReactMultiChild = {
           var mountImage = childInstance.mountComponent(
             rootID,
             transaction,
-            this._mountDepth + 1,
             context
           );
           childInstance._mountIndex = index;
@@ -401,7 +400,6 @@ var ReactMultiChild = {
       var mountImage = child.mountComponent(
         rootID,
         transaction,
-        this._mountDepth + 1,
         context
       );
       child._mountIndex = index;
diff --git a/src/core/__tests__/ReactComponent-test.js b/src/core/__tests__/ReactComponent-test.js
index 3b09fb2f52870..31b15549c84f5 100644
--- a/src/core/__tests__/ReactComponent-test.js
+++ b/src/core/__tests__/ReactComponent-test.js
@@ -16,7 +16,6 @@ var ReactInstanceMap;
 var ReactTestUtils;
 
 var reactComponentExpect;
-var getMountDepth;
 
 describe('ReactComponent', function() {
   beforeEach(function() {
@@ -24,10 +23,6 @@ describe('ReactComponent', function() {
     ReactInstanceMap = require('ReactInstanceMap');
     ReactTestUtils = require('ReactTestUtils');
     reactComponentExpect = require('reactComponentExpect');
-
-    getMountDepth = function(instance) {
-      return ReactInstanceMap.get(instance)._mountDepth;
-    };
   });
 
   it('should throw on invalid render targets', function() {
@@ -231,80 +226,4 @@ describe('ReactComponent', function() {
     var instance = ReactTestUtils.renderIntoDocument(element);
     expect(instance.isMounted()).toBeTruthy();
   });
-
-  it('should know its simple mount depth', function() {
-    var Owner = React.createClass({
-      render: function() {
-        return <Child ref="child" />;
-      }
-    });
-
-    var Child = React.createClass({
-      render: function() {
-        return <div />;
-      }
-    });
-
-    var instance = <Owner />;
-    instance = ReactTestUtils.renderIntoDocument(instance);
-    expect(getMountDepth(instance)).toBe(0);
-    expect(getMountDepth(instance.refs.child)).toBe(1);
-  });
-
-  it('should know its (complicated) mount depth', function() {
-    var Box = React.createClass({
-      render: function() {
-        return <div ref="boxDiv">{this.props.children}</div>;
-      }
-    });
-
-    var Child = React.createClass({
-      render: function() {
-        return <span ref="span">child</span>;
-      }
-    });
-
-    var Switcher = React.createClass({
-      getInitialState: function() {
-        return {tabKey: 'hello'};
-      },
-
-      render: function() {
-        var child = this.props.children;
-
-        return (
-          <Box ref="box">
-            <div
-              ref="switcherDiv"
-              style={{
-                display: this.state.tabKey === child.key ? '' : 'none'
-              }}>
-              {child}
-            </div>
-          </Box>
-        );
-      }
-    });
-
-    var App = React.createClass({
-      render: function() {
-        return (
-          <Switcher ref="switcher">
-            <Child key="hello" ref="child" />
-          </Switcher>
-        );
-      }
-    });
-
-    var root = <App />;
-    root = ReactTestUtils.renderIntoDocument(root);
-
-    expect(getMountDepth(root)).toBe(0);
-    expect(getMountDepth(root.refs.switcher)).toBe(1);
-    expect(getMountDepth(root.refs.switcher.refs.box)).toBe(2);
-    expect(getMountDepth(root.refs.switcher.refs.switcherDiv)).toBe(5);
-    expect(getMountDepth(root.refs.child)).toBe(7);
-    expect(getMountDepth(root.refs.switcher.refs.box.refs.boxDiv)).toBe(3);
-    expect(getMountDepth(root.refs.child.refs.span)).toBe(8);
-  });
 });
diff --git a/src/core/__tests__/ReactCompositeComponent-test.js b/src/core/__tests__/ReactCompositeComponent-test.js
index a8e41988cb9f8..c31c88d462253 100644
--- a/src/core/__tests__/ReactCompositeComponent-test.js
+++ b/src/core/__tests__/ReactCompositeComponent-test.js
@@ -529,6 +529,34 @@ describe('ReactCompositeComponent', function() {
     );
   });
 
+  it('should only allow `setProps` on top-level components', function() {
+    var container = document.createElement('div');
+    document.documentElement.appendChild(container);
+
+    var innerInstance;
+
+    var Component = React.createClass({
+      render: function() {
+        return <div><div ref="inner" /></div>;
+      },
+      componentDidMount: function() {
+        innerInstance = this.refs.inner;
+      }
+    });
+    React.render(<Component />, container);
+
+    expect(innerInstance).not.toBe(undefined);
+    expect(function() {
+      innerInstance.setProps({value: 1});
+    }).toThrow(
+      'Invariant Violation: replaceProps(...): You called `setProps` or ' +
+      '`replaceProps` on a component with a parent. This is an anti-pattern ' +
+      'since props will get reactively updated when rendered. Instead, ' +
+      'change the owner\'s `render` method to pass the correct value as ' +
+      'props to the component where it is created.'
+    );
+  });
+
   it('should cleanup even if render() fatals', function() {
     var BadComponent = React.createClass({
       render: function() {
diff --git a/src/test/ReactTestUtils.js b/src/test/ReactTestUtils.js
index 9b148d188f531..8871a8c12ca29 100644
--- a/src/test/ReactTestUtils.js
+++ b/src/test/ReactTestUtils.js
@@ -340,7 +340,7 @@ ReactShallowRenderer.prototype._render = function(element, transaction, context)
     var instance = new ShallowComponentWrapper(new element.type(element.props));
     instance.construct(element);
 
-    instance.mountComponent(rootID, transaction, 0, context);
+    instance.mountComponent(rootID, transaction, context);
 
     this._instance = instance;
   } else {