The following code illustrates how to destroy secondary windows.

  #define INCL_SW
  #include <os2me.h>

  MRESULT EXPENTRY MyDlgProc (HWND hwnd, ULONG msg, MPARAM mp1, MPARAM m
  {

     switch (msg) {

        case WM_CLOSE:
           /* Destroy a secondary window */
           WinDestroySecondaryWindow (hwndSecondaryFrame);
           return (TRUE);
           break;

     }

     return (WinDefSecondaryWindowProc (hwnd, msg, mp1, mp2));

}