Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As _
  System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
 
                speichern()
    End Sub
 
 
 Private Sub speichern()
 
        Dim sw As New System.IO.StreamWriter(Application.StartupPath & _
          "\Test.txt")
        For Each item As String In ComboBox1.Items
            sw.WriteLine(item)
        Next
        sw.Close()
    End Sub
 
 
Private Sub Laden()
 
        If System.IO.File.Exists(Application.StartupPath & "\Test.txt") Then
            Dim SR As New System.IO.StreamReader(Application.StartupPath & _
              "\Test.txt")
            Do Until SR.EndOfStream
                ComboBox1.Items.Add(SR.ReadLine)
            Loop
            SR.Close()
        End If
    End Sub

Private Sub ComboBox1_KeyDown(ByVal sender As Object, ByVal e As _
  System.Windows.Forms.KeyEventArgs) Handles ComboBox1.KeyDown
 
        If e.KeyCode = Keys.Enter Then
            For i As Integer = 0 To ComboBox1.Items.Count - 1
                If SnomIP_Dropdown.Text = ComboBox1.Items(i).ToString Then
                    MessageBox.Show("Eintrag schon vorhanden")
Exit Sub
                End If
            Next
            ComboBox1.Items.Add(ComboBox1.Text)
            e.Handled = True
        End If
 
    End Sub