The occurrence of squamous change in the bladder epithelium was studied in bladder biopsies from patients with recurrent urinary infections or symptoms of cystitis and comparisons were made with sections taken at necropsy from control subjects. Two types of squamous change, termed `vaginal' and `cornified', are described. Vaginal change was frequent in females, and seemed to be a normal finding in them, but was not observed in males. It did not seem to be caused by urinary infection. Cornified change was also common in females and was found in one (infected) man. Like vaginal change it was most often found in sections from the trigone. Urinary infection may predispose to its formation but we were unable to prove this. Squamous change did not seem to cause symptoms, and could not usually be recognized at cystoscopy. The varieties described are so common that they are unlikely to be markedly precarcinomatous.