How to Access controls on Master Pages from Content Pages in ASP .NET
We will assume that we have a Label control called “Label1” on your Master Page, you might want to change the text of that Label.
To do that write this code in your content page:
Label lbl = new Label(); lbl = (Label)Master.FindControl("Label1"); lbl.Text = "Text";
Of course, this is all assuming the label is OUTSIDE the ContentPlaceHolder