Hi Igor, in Win32 often one passes NULL as argument (for instance if a function has an argument "handle to a window", then a hWnd of NULL can be given). For instance when I have shellExecute: hwnd operation: lpOperation file: lpFile parameters: lpParameters directory: lpDirectory show: nShowCmd <primitive: #primitiveNativeCall module: #NativeBoostPlugin> ^ self nbCall: #( HINSTANCE ShellExecuteA( HWND hwnd, LPCTSTR lpOperation, LPCTSTR lpFile, LPCTSTR lpParameters, LPCTSTR lpDirectory, INT nShowCmd)) module: 'Shell32.dll' The NBFFICallout class(NBNativeCodeGen class)>>handleFailureIn:nativeCode: tells me that "an instance of NBWin32Window" is expected. So currently I have to pass "NBWin32Window getFocus" as first argument. But often this is not necessary. I also havent found a constant pool with NULL or an accessor. Whats the prefered way to deal with NULL in NB? Can you also please add me as a developer to http://www.squeaksource.com/NativeBoost My initials are "tbn" I would like to add several API functions for Win32 (ShellExecute, OutputDebugString, ...) Thx Torsten