Use RegWheelMessage to get the windows message that is sent when the user scrolls the mouse wheel. Typically, applications do not need to use RegWheelMessage. TWinControl checks for this value when it receives window messages, and translates it into appropriate Mouse Wheel events. 

RegWheelMessage is used in Windows 95, but not NT or later versions of Windows. (Mouse support is built into the later operating systems.) 

WheelPresent