Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) _
      Handles MyBase.Load
 
        Dim SubContent As New Form2()
 
        SubContent.TopLevel = False
        Me.Panel1.Controls.Clear()
        SubContent.Parent = Me.Panel1
        SubContent.Dock = DockStyle.Fill
        SubContent.Show()
 
    End Sub

    Private Sub Form2_Load(sender As System.Object, e As System.EventArgs) _
      Handles MyBase.Load
 
        Dim SubContent As New UserControl1()
 
        Me.Panel2.Controls.Clear()
        SubContent.Parent = Me.Panel2
        SubContent.Dock = DockStyle.Fill
        SubContent.Show()
 
    End Sub

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) _
      Handles Button1.Click
 
        Form1.Label1.Text = "HELLO"
        Form2.Label2.Text = "HELLO"
        Form2.CheckBox2.Checked = True
        Form2.TextBox2.Text = "HELLO"
 
    End Sub