Imports System.Threading
Public Class Form1
 
    Private Newform As New Form2
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
 
       Dim Testlauf As New TestClass(Newform)
       Dim Testthread As New Thread(AddressOf Testlauf.Run)
 
       Testthread.Start()
 
    End Sub
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
 
       Newform.Show()
 
    End Sub
 
End Class

Public Class Form2
 
   Public Delegate Sub dlg_lst_Listbox_add(ByVal str_Text As String)
 
   Public Sub lst_Listbox_add(ByVal str_Text As String)
 
        If Me.lst_Listbox.InvokeRequired() Then
            Dim d As New dlg_lst_Listbox_add(AddressOf lst_Listbox_add)
            Me.Invoke(d, New Object() {str_Text})
        Else
            Me.lst_Listbox.Items.Add(str_Text)
        End If
 
    End Sub
 
End Class

Public Class TestClass
    Private aktForm2 As Form2
 
    Public Sub New(ByVal _aktForm2 As Form2)
 
        aktForm2 = _aktForm2
 
    End Sub
 
    Public Sub Run()
 
        aktForm2.lst_Listbox_add("Text von Thread aus eingefügt")
 
    End Sub
End Class