If you want to use SendMessage to send something to a window, do what was mentioned above. Maybe inherit a NativeWindow, and set the caption to something like "My Special Window". Then you can use FindWindow("My Special Window") to find the handle of the window you want to SendMessage to. All you need to do then is override WndProc in the NativeWindow. Have a look at FindWindow on pinvoke.net. www.andrewvos.com