diff --git a/packages/spark/spark.js b/packages/spark/spark.js
index 312ac73e66..ad41e97b31 100644
--- a/packages/spark/spark.js
+++ b/packages/spark/spark.js
@@ -136,6 +136,15 @@ Spark.isolate = function (htmlFunc) {
     renderer.annotate(ctx.run(htmlFunc), "_isolate", function (range) {
       ctx.on_invalidate(function () {
         // XXX update with patching
+        var frag = Spark.render(function () {
+          return Spark.isolate(htmlFunc);
+        });
+        var oldContents = range.replace_contents(frag); // (should patch)
+        range.destroy();
+        // (GC oldContents)
+
+        // later:
+        // GC, rewire, patching, etc.
       });
     });
 
diff --git a/packages/spark/spark_tests.js b/packages/spark/spark_tests.js
index 38ad86b69c..cf6ed33c2c 100644
--- a/packages/spark/spark_tests.js
+++ b/packages/spark/spark_tests.js
@@ -64,3 +64,25 @@ Tinytest.add("spark - assembly", function (test) {
   test.isTrue(attrValue.indexOf('abc<!--') === 0, attrValue);
   test.isTrue(attrValue.indexOf('-->xyz') >= 0, attrValue);
 });
+
+
+Tinytest.add("spark - basic isolate", function (test) {
+
+  var R = ReactiveVar('foo');
+
+  var div = OnscreenDiv(Spark.render(function() {
+    return '<div>' + Spark.isolate(function() {
+      return '<span>' + R.get() + '</span>';
+    }) + '</div>';
+  }));
+
+  test.equal(div.html(), '<div><span>foo</span></div>');
+  R.set('bar');
+  test.equal(div.html(), '<div><span>foo</span></div>');
+  Meteor.flush();
+  test.equal(div.html(), '<div><span>bar</span></div>');
+  R.set('baz');
+  Meteor.flush();
+  test.equal(div.html(), '<div><span>baz</span></div>');
+  
+});
\ No newline at end of file