how can i pass value from master page to content page and vice versa ?

//on master pag
Label lbl =(Label) Page.Master.FindControl("ContentPlaceHolder1").FindControl("lblm"); lbl.Text =
"hgfgc";//lbm  label on aspx pages within ContentPlaceHolder1 id



//how can i pass value from content page  to  master page  ?
//on aspx pages
Label lbl = (Label)this.Master.FindControl("lblm");lbl.Text =
"hgfgc";
//lbm lable on master pages