[DllImport("USER32")] private static extern short GetKeyState(int vkey); private const int VK_LBUTTON = 0x01; private void timer1_Tick(object sender, System.EventArgs e) { if ((GetKeyState(VK_LBUTTON)<0)) { label1.Text +=VK_LBUTTON; } else { label2.Text += VK_LBUTTON + 1; } }