diff --git a/core/block.js b/core/block.js
index bec24df49..53b7ba1b1 100644
--- a/core/block.js
+++ b/core/block.js
@@ -46,11 +46,16 @@ goog.require('goog.string');
  * @param {!Blockly.Workspace} workspace The block's workspace.
  * @param {?string} prototypeName Name of the language object containing
  *     type-specific functions for this block.
+ * @param {=string} opt_id Optional ID.  Use this ID if provided, otherwise
+ *     create a new id.
  * @constructor
  */
-Blockly.Block = function(workspace, prototypeName) {
+Blockly.Block = function(workspace, prototypeName, opt_id) {
   /** @type {string} */
-  this.id = Blockly.genUid();
+  this.id = opt_id || Blockly.genUid();
+  goog.asserts.assert(!Blockly.Block.getById(this.id),
+      'Error: Block "%s" already exists.', this.id);
+  Blockly.Block.BlockDB_[this.id] = this;
   /** @type {Blockly.Connection} */
   this.outputConnection = null;
   /** @type {Blockly.Connection} */
@@ -140,20 +145,6 @@ Blockly.Block.obtain = function(workspace, prototypeName) {
  */
 Blockly.Block.prototype.data = null;
 
-/**
- * Get an existing block.
- * @param {string} id The block's id.
- * @param {!Blockly.Workspace} workspace The block's workspace.
- * @return {Blockly.Block} The found block, or null if not found.
- */
-Blockly.Block.getById = function(id, workspace) {
-  if (Blockly.Realtime.isEnabled()) {
-    return Blockly.Realtime.getBlockById(id);
-  } else {
-    return workspace.getBlockById(id);
-  }
-};
-
 /**
  * Dispose of this block.
  * @param {boolean} healStack If true, then try to heal any gap by connecting
@@ -201,10 +192,8 @@ Blockly.Block.prototype.dispose = function(healStack, animate,
     }
     connections[i].dispose();
   }
-  // Remove from Realtime set of blocks.
-  if (Blockly.Realtime.isEnabled() && !Blockly.Realtime.withinSync) {
-    Blockly.Realtime.removeBlock(this);
-  }
+  // Remove from block database.
+  delete Blockly.Block.BlockDB_[this.id];
 };
 
 /**
@@ -1240,3 +1229,19 @@ Blockly.Block.prototype.getRelativeToSurfaceXY = function() {
 Blockly.Block.prototype.moveBy = function(dx, dy) {
   this.xy_.translate(dx, dy);
 };
+
+/**
+ * Database of all blocks.
+ * @private
+ */
+Blockly.Block.BlockDB_ = Object.create(null);
+
+/**
+ * Find the block with the specified ID.
+ * @param {string} id ID of block to find.
+ * @return {Blockly.Block} The sought after block or null if not found.
+ */
+Blockly.Block.getById = function(id) {
+  return Blockly.Block.BlockDB_[id] || null;
+};
+
diff --git a/core/block_svg.js b/core/block_svg.js
index fa66ed4a2..15af148cc 100644
--- a/core/block_svg.js
+++ b/core/block_svg.js
@@ -40,11 +40,14 @@ goog.require('goog.math.Coordinate');
  * @param {!Blockly.Workspace} workspace The block's workspace.
  * @param {?string} prototypeName Name of the language object containing
  *     type-specific functions for this block.
+ * @param {=string} opt_id Optional ID.  Use this ID if provided, otherwise
+ *     create a new id.
  * @extends {Blockly.Block}
  * @constructor
  */
-Blockly.BlockSvg = function(workspace, prototypeName) {
-  Blockly.BlockSvg.superClass_.constructor.call(this, workspace, prototypeName);
+Blockly.BlockSvg = function(workspace, prototypeName, opt_id) {
+  Blockly.BlockSvg.superClass_.constructor.call(this,
+      workspace, prototypeName, opt_id);
   // Create core elements for the block.
   /** @type {SVGElement} */
   this.svgGroup_ = Blockly.createSvgElement('g', {}, null);
diff --git a/core/generator.js b/core/generator.js
index 664a037b1..082101b40 100644
--- a/core/generator.js
+++ b/core/generator.js
@@ -202,6 +202,8 @@ Blockly.Generator.prototype.valueToCode = function(block, name, order) {
   }
   // Value blocks must return code and order of operations info.
   // Statement blocks must only return code.
+  goog.asserts.assertArray(tuple, 'Expecting tuple from value block "%s".',
+      targetBlock.type);
   var code = tuple[0];
   var innerOrder = tuple[1];
   if (isNaN(innerOrder)) {
@@ -237,6 +239,7 @@ Blockly.Generator.prototype.statementToCode = function(block, name) {
   var code = this.blockToCode(targetBlock);
   // Value blocks must return code and order of operations info.
   // Statement blocks must only return code.
+  goog.asserts.assertString(code, 'Expecting code from statement block "%s".',
       targetBlock && targetBlock.type);
   if (code) {
     code = this.prefixLines(/** @type {string} */ (code), this.INDENT);
diff --git a/core/workspace.js b/core/workspace.js
index 84874d9f3..ac62f3fd2 100644
--- a/core/workspace.js
+++ b/core/workspace.js
@@ -152,10 +152,12 @@ Blockly.Workspace.prototype.getWidth = function() {
  * Obtain a newly created block.
  * @param {?string} prototypeName Name of the language object containing
  *     type-specific functions for this block.
+ * @param {=string} opt_id Optional ID.  Use this ID if provided, otherwise
+ *     create a new id.
  * @return {!Blockly.Block} The created block.
  */
-Blockly.Workspace.prototype.newBlock = function(prototypeName) {
-  return new Blockly.Block(this, prototypeName);
+Blockly.Workspace.prototype.newBlock = function(prototypeName, opt_id) {
+  return new Blockly.Block(this, prototypeName, opt_id);
 };
 
 /**
diff --git a/core/workspace_svg.js b/core/workspace_svg.js
index e5d23afd2..73f2ada76 100644
--- a/core/workspace_svg.js
+++ b/core/workspace_svg.js
@@ -250,10 +250,12 @@ Blockly.WorkspaceSvg.prototype.dispose = function() {
  * Obtain a newly created block.
  * @param {?string} prototypeName Name of the language object containing
  *     type-specific functions for this block.
+ * @param {=string} opt_id Optional ID.  Use this ID if provided, otherwise
+ *     create a new id.
  * @return {!Blockly.BlockSvg} The created block.
  */
-Blockly.WorkspaceSvg.prototype.newBlock = function(prototypeName) {
-  return new Blockly.BlockSvg(this, prototypeName);
+Blockly.WorkspaceSvg.prototype.newBlock = function(prototypeName, opt_id) {
+  return new Blockly.BlockSvg(this, prototypeName, opt_id);
 };
 
 /**
@@ -445,7 +447,7 @@ Blockly.WorkspaceSvg.prototype.highlightBlock = function(id) {
   }
   var block = null;
   if (id) {
-    block = this.getBlockById(id);
+    block = Blockly.Block.getById(id);
     if (!block) {
       return;
     }
diff --git a/core/xml.js b/core/xml.js
index 8f54b1b5b..db9e0e497 100644
--- a/core/xml.js
+++ b/core/xml.js
@@ -295,14 +295,11 @@ Blockly.Xml.domToWorkspace = function(workspace, xml) {
  * workspace.
  * @param {!Blockly.Workspace} workspace The workspace.
  * @param {!Element} xmlBlock XML block element.
- * @param {boolean=} opt_reuseBlock Optional arg indicating whether to
- *     reinitialize an existing block.
  * @return {!Blockly.Block} The root block created.
  */
-Blockly.Xml.domToBlock = function(workspace, xmlBlock, opt_reuseBlock) {
+Blockly.Xml.domToBlock = function(workspace, xmlBlock) {
   // Create top-level block.
-  var topBlock = Blockly.Xml.domToBlockHeadless_(workspace, xmlBlock,
-                                                 opt_reuseBlock);
+  var topBlock = Blockly.Xml.domToBlockHeadless_(workspace, xmlBlock);
   if (workspace.rendered) {
     // Hide connections to speed up assembly.
     topBlock.setConnectionsHidden(true);
@@ -334,37 +331,17 @@ Blockly.Xml.domToBlock = function(workspace, xmlBlock, opt_reuseBlock) {
  * workspace.
  * @param {!Blockly.Workspace} workspace The workspace.
  * @param {!Element} xmlBlock XML block element.
- * @param {boolean=} opt_reuseBlock Optional arg indicating whether to
- *     reinitialize an existing block.
  * @return {!Blockly.Block} The root block created.
  * @private
  */
-Blockly.Xml.domToBlockHeadless_ =
-    function(workspace, xmlBlock, opt_reuseBlock) {
+Blockly.Xml.domToBlockHeadless_ = function(workspace, xmlBlock) {
   var block = null;
   var prototypeName = xmlBlock.getAttribute('type');
   if (!prototypeName) {
     throw 'Block type unspecified: \n' + xmlBlock.outerHTML;
   }
   var id = xmlBlock.getAttribute('id');
-  if (opt_reuseBlock && id) {
-    // Only used by realtime.
-    block = Blockly.Block.getById(id, workspace);
-    // TODO: The following is for debugging.  It should never actually happen.
-    if (!block) {
-      throw 'Couldn\'t get Block with id: ' + id;
-    }
-    var parentBlock = block.getParent();
-    // If we've already filled this block then we will dispose of it and then
-    // re-fill it.
-    if (block.workspace) {
-      block.dispose(true, false, true);
-    }
-    block.fill(workspace, prototypeName);
-    block.parent_ = parentBlock;
-  } else {
-    block = workspace.newBlock(prototypeName);
-  }
+  block = workspace.newBlock(prototypeName, id);
 
   var blockChild = null;
   for (var i = 0, xmlChild; xmlChild = xmlBlock.childNodes[i]; i++) {
@@ -453,7 +430,7 @@ Blockly.Xml.domToBlockHeadless_ =
         }
         if (childBlockNode) {
           blockChild = Blockly.Xml.domToBlockHeadless_(workspace,
-              childBlockNode, opt_reuseBlock);
+              childBlockNode);
           if (blockChild.outputConnection) {
             input.connection.connect(blockChild.outputConnection);
           } else if (blockChild.previousConnection) {
@@ -475,7 +452,7 @@ Blockly.Xml.domToBlockHeadless_ =
             throw 'Next statement is already connected.';
           }
           blockChild = Blockly.Xml.domToBlockHeadless_(workspace,
-              childBlockNode, opt_reuseBlock);
+              childBlockNode);
           if (!blockChild.previousConnection) {
             throw 'Next block does not have previous statement.';
           }
diff --git a/tests/jsunit/block_test.js b/tests/jsunit/block_test.js
new file mode 100644
index 000000000..a799340bc
--- /dev/null
+++ b/tests/jsunit/block_test.js
@@ -0,0 +1,35 @@
+/**
+ * @license
+ * Blockly Tests
+ *
+ * Copyright 2015 Google Inc.
+ * https://developers.google.com/blockly/
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+'use strict';
+
+function test_getById() {
+  var workspace = new Blockly.Workspace();
+  var blockA = workspace.newBlock('');
+  var blockB = workspace.newBlock('');
+  assertEquals('Find blockA.', blockA, Blockly.Block.getById(blockA.id));
+  assertEquals('Find blockB.', blockB, Blockly.Block.getById(blockB.id));
+  assertEquals('No block found.', null,
+      Blockly.Block.getById('I do not exist.'));
+  blockA.dispose();
+  assertEquals('Can\'t find blockA.', null, Blockly.Block.getById(blockA.id));
+  assertEquals('BlockB exists.', blockB, Blockly.Block.getById(blockB.id));
+  workspace.clear();
+  assertEquals('Can\'t find blockB.', null, Blockly.Block.getById(blockB.id));
+}
diff --git a/tests/jsunit/index.html b/tests/jsunit/index.html
index f2e48cbfc..9c3df0ea6 100644
--- a/tests/jsunit/index.html
+++ b/tests/jsunit/index.html
@@ -8,6 +8,7 @@
   </head>
   <body>
     <script src="blockly_test.js"></script>
+    <script src="block_test.js"></script>
     <script src="connection_test.js"></script>
     <script src="generator_test.js"></script>
     <script src="names_test.js"></script>
diff --git a/tests/jsunit/workspace_test.js b/tests/jsunit/workspace_test.js
index f4237a8a2..cf18f162e 100644
--- a/tests/jsunit/workspace_test.js
+++ b/tests/jsunit/workspace_test.js
@@ -66,17 +66,3 @@ function test_maxBlocksWorkspace() {
   workspace.clear();
   assertEquals('Cleared capacity.', 0, workspace.remainingCapacity());
 }
-
-function test_getByIdWorkspace() {
-  var workspace = new Blockly.Workspace();
-  var blockA = workspace.newBlock('');
-  var blockB = workspace.newBlock('');
-  assertEquals('Find blockA.', blockA, workspace.getBlockById(blockA.id));
-  assertEquals('Find blockB.', blockB, workspace.getBlockById(blockB.id));
-  assertEquals('No block found.', null, workspace.getBlockById('I do not exist.'));
-  blockA.dispose();
-  assertEquals('Can\'t find blockA.', null, workspace.getBlockById(blockA.id));
-  assertEquals('BlockB exists.', blockB, workspace.getBlockById(blockB.id));
-  workspace.clear();
-  assertEquals('Can\'t find blockB.', null, workspace.getBlockById(blockB.id));
-}