Sub Form_Load()
Combo1.AddItem "Item 1"
Combo1.AddItem "Item 2"
Combo1.AddItem "Item 3"
End Sub
Private Sub Command1_Click()
Dim r as Long
r = SendMessageLong(Combo1.hWnd, CB_SHOWDROPDOWN, True, 0)
End Sub

Private Sub Command2_Click()
Dim r as Long
r = SendMessageLong(Combo1.hWnd, CB_SHOWDROPDOWN, False, 0)
End Sub