>Usually the GetWindowLong is used to obtain it.

Yes, the first parameter is got this way in the class bindwindowsevetnsproxy.init

This._WindowProc = apiGetWindowLong(_vfp.HWnd, GWL_WNDPROC)

I confirmed the first parameter by calling apiGetWindowLong just before the call to apiCallWindowProc and the value returned by Long and the parameter passed to Proc is the same.

Thanks for responding. Please advise.