From November 1986 through May 1989, a Food and Drug Administration approved investigational study was done to assess the safety and efficacy of glutaraldehyde cross-linked bovine dermal collagen in the endoscopic treatment of vesicoureteral reflux. Over-all, 57 patients (92 ureters) were treated. The majority of ureters (68.5%) had grade II to III/V vesicoureteral reflux (international classification). One treatment was given in 61.4% of the patients, while 33.3% required 2 and 5.3% required 3 treatments. Nonduplicated/primarily refluxing ureters comprised 68.5% of the total, while 13% were duplex/primarily refluxing and 18.5% were surgical failures. The procedures were performed on an outpatient basis in all but 3 patients. Patients were evaluated by voiding cystourethrogram and renal/bladder sonography before and after treatment at 1 month and 1 year. Cure at 1 month after the last treatment was achieved in 75% of the ureters. Among the ureters cured at 1 month the cure persisted in 79% at 1 year after treatment. Cure at 1 year was achieved in 65% of all ureters evaluated, regardless of the status at 1 month. Procedure-related morbidity was minimal and there were no adverse reactions to the implant substance. Thus, glutaraldehyde cross-linked bovine dermal collagen appears to be safe and effective in the endoscopic treatment of vesicoureteral reflux.