After we treated our carpets with the recipe, I noticed that the carpets didn't smell of cat urine odor anymore but I could still smell it in the room. I couldn't figure out where it was coming from.

Back to the computer and the internet. Many people where recommending a black light to locate the cat urine, especially for areas that where already dried as cat urine can be invisible when dried.

I bought a black light from Home Depot and found that the previous owners' cat had also sprayed on the walls, doors and floorboards of the rooms! I would have never known had I not purchased one. Cat urine glows under ultraviolet light a pale flourescent yellow, like a blacklight poster does.

I had a hard time seeing all the urine over such a large area with the black light I purchased from Home Depot so ended up purchasing a brighter one from Utimate Pet Products. This one had 2 blacklight bulbs in it and kept me from having to get so close to the carpet and the smell!

Make sure the room is as dark as possible, preferrably at night. Turn the light on and you will see bright pale yellow spots where the urine is. Either mark the area with masking tape to identify it or do as I did, spray as you go (my husband held the black light while I sprayed the spot throughly).

The black light is also invaluable for checking to see if there is anymore cat urine left on the spots you have treated, to see if they need to be retreated.