Dye Pills to Identify Cat Urine

By Jane Meggitt

You know that one of your felines is peeing in the house but you aren't sure who is the guilty party. Your vet can prescribe pills or give each cat an injection with a dye that will show up in his urine. The dye doesn't hurt the cat and will let you identify who needs help. One caveat: It can stain.

Urine Marking

Cats start soiling in the house for a variety of reasons. Neutering or spaying your cat might solve the problem, but otherwise you must look for physical or emotional issues. Your vet should examine your cats to make sure they aren't suffering from kidney or bladder issues. Provide ample litter boxes for your feline family -- ideally, one per cat plus one. Keep the boxes scrupulously clean. Experiment with different brands and types of litter, as some cats definitely have preferences that you'll do well to meet. If none of those efforts work, and you never catch the cat who's soiling the house, it's time to go the fluorescein dye route.

Fluorescein Dye Pills

Your vet can prescribe fluorescein dye pills, generally at a dosage level of 50 milligrams per feline. She can also inject your cat with a version of the dye. According to an article written by Dr. Jacqueline C. Neilson in the journal "Clinical Techniques in Small Animal Practice," another alternative is making oral capsules from opthalmic strips impregnated with fluorescein. This is accomplished by tearing off the orange part of a strip, which contains fluorescein, and folding it into a gelatin capsule. Fold six 9-milligram strips into each capsule and administer to the cat.

Finding the Guilty Party

If you have a suspicion about who is soiling the house, start the fluorescein treatment with that cat. Within 24 hours of receiving fluorescein, a cat's urine will appear bright green when viewed with a fluorescent black light, which you can buy at a pet store. This process of feline elimination -- no pun intended -- depends on how many cats you have in the household and how quickly you find the guilty party. Once you know who's causing the problem, you can take him to the vet for further testing or evaluate possible reasons for the soiling. If the culprit is bullied by other cats, he might be taking it out on your rugs.


If your cat is soiling light-colored carpeting or furniture, think twice about using dye pills. It's possible that the offending cat's urine will stain the items. Of course, regular urine leaves stains, as well -- but it isn't bright green. Even after vigorous cleaning, you might still be able to spot the dye. If the dye pills leave stains, you might need to hire professional cleaners to get rid of them.