Sorry, you are right. I believe what is going on is that upon the user clicking and dragging inside the window, WM_CAPTURECHANGED is received indicating that the mouse capture has been released (that's probably what lParam=0 means). The problem, then, is that WM_MOUSEMOVE messages are being posted on the event-queue but my WindowProc never receives them. I am subclassing some other window. My guess is that the window calls GetMessage(), sees WM_MOUSEMOVE, and handles it internally without passing it on to the WindowProc. This poses a problem for me because I absolutely must subclass WM_MOUSEMOVE. Any ideas? Gili

Hi, I am getting WM_CAPTURECHANGED messages with lParam=0 and then my WindowProc stops getting messages (because my focus has disappeared). How is this legal? lParam is supposed to contain the HWND of the window that stole focus away from my WindowProc but it is zero which is an illegal value. How do I find out who has taken focus? Is this documented anywhere? Thank you, Gili