Hi, I think I found the answer: 1. Use vtkInteractorStyleTrackballCamera for m_pvtkWin32RenderWI's SetInteractorStyle 2. Use "return vtkHandleMessage2(m_hWnd, message, wParam, lParam, m_pvtkWin32RenderWI);" Which means the m_hWnd of the dialog and not of the dialog element. sorry for bothering... greets Ingo