Public Class Form1
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        'http://msdn2.microsoft.com/de-de/library/system.windows.forms.maskedte
        ' xtbox.mask(VS.80).aspx
        'nur buchstaben
        Me.MaskedTextBox1.Mask = "LLLL"
 
    End Sub
 
    Private Sub MaskedTextBox1_KeyPress(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.KeyPressEventArgs) Handles MaskedTextBox1.KeyPress
        If Char.IsLetter(e.KeyChar) AndAlso Not Char.IsUpper(e.KeyChar) Then
            e.Handled = True
            Me.MaskedTextBox1.AppendText(Char.ToUpper(e.KeyChar))
            MyBase.OnKeyPress(New KeyPressEventArgs(Char.ToUpper(e.KeyChar)))
        End If
    End Sub
 
    Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
        If Char.IsLetter(e.KeyChar) AndAlso Not Char.IsUpper(e.KeyChar) Then
            e.Handled = True
            Me.TextBox1.AppendText(Char.ToUpper(e.KeyChar))
            MyBase.OnKeyPress(New KeyPressEventArgs(Char.ToUpper(e.KeyChar)))
        End If
    End Sub
End Class