How to detect mouse wheel tilt?

To detect rotation of the mouse wheel in .NET/WinForms, I can override OnMouseWheel. Clicking can be detected by overriding OnMouseDown (it’s just the Middle button). But how do I detect tilting of the wheel (tilt to the left/right for horizontal scrolling)? Neither OnMouseWheel, not OnMouseDown is being called when I tilt the mouse wheel.

Covered here; in short, you need to handle the windows message manually (at it isn’t handled directly in .NET – code is from the linked article):

    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);
        if (m.HWnd != this.Handle)
        {
            return;
        }
        switch (m.Msg)
        {
            case Win32Messages.WM_MOUSEHWHEEL:
                FireMouseHWheel(m.WParam, m.LParam);
                m.Result = (IntPtr)1;
                break;
            default:
                break; 
        }
    }
    ...
    abstract class Win32Messages
    {
        public const int WM_MOUSEHWHEEL = 0x020E;//discovered via Spy++
    }

Based on this article, if you have the IntelliPoint drivers, you will get WM_MOUSEHWHEEL messages.