Quick Overview: When you have done your best cleaning and the yellow urine stain remains, Pros Choice Urine Stain Remover is the answer. Simply spray USR on the stain and watch it disappear. Urine Stain Remover is self neutralizing on all synthetic fibers but is not recommended for use on natural fibers like cotton, wool, or silk. Directions: Thoroughly clean stained area first. Following cleaning, apply Urine Stain Remover full strength directly to urine stain. The time required for complete reaction to occur and for the stain to disappear will vary from 3 to 8 hours depending on the temperature of the carpet. Repeat treatment if necessary.