Code:

TSMemo = class(TMemo)

procedure WM_HScroll(var Msg: TWMHScroll); message WM_HSCROLL;

procedure WM_VScroll(var Msg: TWMVScroll); message WM_VSCROLL;

end;

...

procedure TSMemo.WM_HScroll(var Msg: TWMHScroll);

begin

ShowMessage('HScroll');

end;

procedure TSMemo.WM_VScroll(var Msg: TWMVScroll);

begin

ShowMessage('VScroll');

end;