Public Class frmMDI
    Friend frmDel As Form
    Friend frmAdd As Form

    Private Sub Sockel_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles tsbFarbdetailsSo.Click
 
        If IsFormPresent("frmSo", eFormSearch.Name, eFormAction.BringToFront) _
          Then
            '-------
            Exit Sub
            '-------
        End If
 
        ' Form
        Dim frm As New Form
        frm.Name = "frmSo"
        frm.MdiParent = Me
        frm.WindowState = FormWindowState.Maximized
        frm.Text = "Sockel"
 
        ' Usercontrol
        Dim uc As UC_Sockel
        uc = New UC_Sockel()
        uc.Dock = DockStyle.Fill
        frm.Controls.Add(uc)
        frm.Show()
 
        frmDel.BringToFront()
        frmAdd.BringToFront()
 
    End Sub

...            ' kleine Forms in UC_Sockel aufrufen
            frmMDI.frmAdd = New Add_Sockel()
            frmMDI.frmDel = New DEL_Sockel()

          'Anweisungen in DEL_Sockel (da sie sich sofort schließt wenn sie 
          ' keine Datensätze enthält)  
                Me.Show()
                Me.BringToFront()
                Me.MdiParent = frmMDI
                Me.WindowState = FormWindowState.Normal