Private Sub Text1_KeyPress(KeyAscii As Integer)
Dim Worte() As String
Dim N As Integer
 
Select Case KeyAscii
 
  Case 8 ' Backspace
 
  Case Asc("a"), Asc("A")
 
  Case Else
 
    Worte = Split(Text1.Text, ",")
 
    If UBound(Worte) = -1 Then
      KeyAscii = 0
    End If
 
    For N = 0 To UBound(Worte)
      If LCase(Mid(Worte(N), 1, 1)) <> "a" Then
        KeyAscii = 0
      End If
    Next
 
End Select
 
End Sub