PURPOSE: To evaluate the efficacy of acetic acid as a sclerosing agent by observation of histologic change in urinary bladder epithelium after the instillation of acetic acid. MATERIALS AND METHODS: Urinary bladder of the rabbit was catheterized with a Foley catheter, and acetic acid of 10%, 20%, 30%, 40% and 50% concentration was instilled for 5 minutes. After evacuation of the acid, the bladder was irrigated three times with normal saline. After two days, gross and histologic examinations of the bladder were performed. RESULTS: A bladder into which10% acetic acid had been instilled revealed a nearly normal epithelium without denudation. In two cases, 20% acetic acid was instilled; one revealed partial denudation of the epithelium and the other revealed complete denudation. Mild to moderate interstitial edema and vascular congestion of the bladder wall were evident in all cases in which acid at a concentration of 30% or more had been instilled. In all cases in which the concentration of acid was greater than 30%, the epithelium was completely denuded. CONCLUSION: An acetic acid concentration of 40% or more is sufficient to completely destroy the epithelium of rabbit urinary bladder, and may be effective as a new sclerosing agent in cases of renal or hepatic cyst.