Cystotomies were performed on mature guinea pigs using aseptic technique, and one layer closure with polypropylene sutures. It was found that epithelialization over the suture material was completed by 3 days and that epithelialization of the bladder mucosa itself after a mucosa-mucosa approximation was completed within 4 days. The main significance of this investigation is that the normal bladder mucosa was completely healed within 4 days.