ok , in Form3 ( to load Form4 ) do this :
VB Code:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim frm4 As New Form4()
AddOwnedForm(frm4) '/// make form4 owned by form3.
frm4.Show()
End Sub
in Form4 ( to send some text back to Form3 ) do this :
VB Code:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim frm3 As Form3 = Me.Owner
frm3.TextBox1.Text = "some text from form4!"
End Sub
to make it easier i've thrown an example together.