Accessing ASP.NET controls within an IFRAME in CRM 4.0

There was a requirement to disable an drop-down list which was in an IFRAME in a CRM form.

The below code allowed me to access the value of the ASP.NET drop-down list:

document.frames.IFRAME_Test.document.all.DropDownList1.value;

and the below code allowed me to disable it:

document.frames.IFRAME_Test.document.all.DropDownList1.disabled= true;