How to make Read Only field.

I have added two buttons on a form "PO Return" and "non PO Return" here....

function CHECK_OnClick(id, row)
{
 if(id == "check1")
 {
  //Getting data value from check box 0 or 1
  alert ("po return");
//  Disp="R" nm="Submit" value="R" nbr="_111" id="label110" visable="0"
  POForm();
  
 }
 if(id == "check2")
 {
         alert ("nonpo return");
         NonPOForm();
 }
}



The Alerts word fine when clicking the form, however I would like to supress the Requesting Location field on my form which is TEXT11 _f20.     I would also like to make another field read only.... OUT5 _f18

Thanks...