How do you clean feather or down pillows that a cat has urinated on?

If can remove the pillow cover , do so. Buy a product found in pet supply stores called Simple Solutions EXTREME and saturate the pillow cover with the product, it's a spray. Spray the pillow insert itself too withe same spray. Most if not all the smell should be gone with the first try, the pillow cover will dry. You could wash the cover if washable, or dry clean it. Though neither will get rid of all the smell , but it will make you feel that it is cleaner. If the pillow insert is really bad, you could for very little money replace the insert. Measure it and look on line there are plenty of retailer's on line who sell 5% down , 90% feather inserts. Some are well under $10.00. I personally feel that cats are very attracted to the smell of feather pillows in general.