Public Class Form1
    Declare Function WindowFromPoint Lib "user32" (ByVal xyPoint As Point) As _
      IntPtr
    Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd _
    As IntPtr, ByVal wMsg As Integer, _
                     ByVal wParam As Integer, ByVal lParam As String) As Integer
    Const WM_VSCROLL As Int32 = &H115
    Const SB_DOWN As Int32 = 1        ' 1 Eintrag nach unten
    Const SB_BOTTOM As Int32 = 7      ' ganz nach unten
 
    Private Sub ComboBox1_MouseUp(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.MouseEventArgs) Handles ComboBox1.MouseUp
        Dim r As Rectangle = RectangleToScreen(ComboBox1.Bounds)
        For i As Int32 = 1 To 70
            SendMessage(WindowFromPoint(New Point(r.X + 10, r.Y + 25)), _
              WM_VSCROLL, SB_DOWN, Nothing)
            Application.DoEvents()
            Threading.Thread.Sleep(50)
        Next
    End Sub
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        For i As Int32 = 1 To 50
            ComboBox1.Items.Add(i.ToString)
        Next
    End Sub
End Class