Actually, you're right in what you say. I accidently passed the HWND of the MDI window to the function, sorry.

Either way, it still doesn't work. GetTopWindow(mwnd) now only returns one single number, no matter which window is the active one. frown

Code:
function getactivehwnd(mwnd,awnd:hwnd;data,parms:pchar;show,nopause:boolean):integer;stdcall;
begin
  strcopy(data,pchar(inttostr(GetTopWindow(mwnd))));
  result:=3;
end;