Here is code that I am going to put into a Framework so I can use the mouse wheel. Now I just need to get Reading and Writing TIFF files working. case kEventClassMouse:{ switch ( GetEventKind(inEvent) ) { case kEventMouseWheelMoved: { OSStatus status; UInt32 modifiers; EventMouseWheelAxis axis; SInt32 delta; status = GetEventParameter( inEvent, kEventParamKeyModifiers, typeUInt32, NULL, sizeof(modifiers), NULL, &modifiers ); ASSERT_NO_ERR(status); status = GetEventParameter( inEvent, kEventParamMouseWheelAxis, typeMouseWheelAxis, NULL, sizeof(axis), NULL, &axis ); ASSERT_NO_ERR(status); status = GetEventParameter( inEvent, kEventParamMouseWheelDelta, typeLongInteger, NULL, sizeof(delta), NULL, &delta ); ASSERT_NO_ERR(status); if ( axis == kEventMouseWheelAxisY ) { SInt32 deltaPixels = 40 * delta; if (modifiers & optionKey) deltaPixels *= 10; this->ScrollVertically( -deltaPixels ); result = noErr; } break; } } break;}