Public Class Form1
    Inherits System.Windows.Forms.Form
#Region " Vom Windows Form Designer generierter Code "
[....]
#End Region
    Private Sub TabControl1_KeyUp(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.KeyEventArgs) Handles TabControl1.KeyUp
        If e.KeyCode = Keys.Tab Then
            Static i As Integer
            i += 1
            If i = Me.TabControl1.TabCount - 1 Then
                RemoveHandler TabControl1.Validating, AddressOf _
                  Me.TabControl1_Validating
            End If
            If i = Me.TabControl1.TabCount Then
                i = 0
                Me.GetNextControl(Me, True).Focus()
                AddHandler TabControl1.Validating, AddressOf _
                  Me.TabControl1_Validating
            End If
            Me.TabControl1.SelectedIndex = i
        End If
    End Sub
    Private Sub TabControl1_Validating(ByVal sender As Object, ByVal e As _
      System.ComponentModel.CancelEventArgs) Handles TabControl1.Validating
        CType(sender, TabControl).Focus()
    End Sub
End Class