Bind Dropdownlist of Parent form after closing the child form

Hi all,
I have a parent and a child form.
I am calling child form on a radiobutton list event.
protected void RadioButtonList1_SelectedIndexChanged(object sender, EventArgs e) { Page.ClientScript.RegisterStartupScript(this.GetType(), "openwindow", "window.open('test.aspx','_blank','top=200, height=200');", true); } there is a button named submit on my child form which is test.aspx.
There a a bounded dropdownlist in my parent form, I want that when i click submit button of child form, the dropdownlist on parent form should be rebind.
how to do that?