I am having the same problem. I am calling the FileWatcher component in the .NET framework from a server (middleware) class. If I place this on a form, I'm set, I just hand the FileWatcher class a reference to my form. The file watcher class then calls the form's Invoke method. However I don't have a form, so am forced to implement the ISynchronizeInvoke interface myself. Your suggestion to go look at the mono project seems like a good start. Can you tell me where to find this project? My solution so far is to implement ISnychronizeInvoke and to create an delegate instance that will be executed when the callback is executed. 1. I register a call back. 2. The call back is executed. The sender is the operating system. 3. I then execute a delegate that I instantiated on the "target" thread. David Minor Applications Programmer NC State Archives