Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
   (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As _
   Any) As Long
 
Const EM_GETLINECOUNT = &HBA
 
Private Sub RTB_Change()
   If SendMessage(RTB.hWnd, EM_GETLINECOUNT, 0, 0&) > 9 Then
      Text1.Text = "Eine Zeile zuviel"
   Else
      Text1.Text = "Noch eine"
   End If
End Sub