Animal studies indicate that 13-cis-retinoic acid (CRA) inhibits bladder tumor growth and is effective in treating patients with serious dermatologic disorders. A trial of CRA in patients at high risk for recurrent Ta, T1 tumors was initiated at an experimental dose of 0.5 mg/kg/d in three divided doses, increasing to 1 mg/kg/d at four weeks. Treatment of twenty eligible patients lasted for six months with an additional 24 month follow-up period. One patient was later excluded due to toxicity resulting in an early dose reduction. Eight patients stopped treatment before three months; of these five, had recurrences within three months, one developed pulmonary metastasis, and one developed a T2G3 tumor. Four patients stopped treatment between three and six months; three of them had recurrences before one year and one had no evidence of disease at seven years. Seven patients completed the course; of these three had recurrences within six months, and three more had recurrences at 8, 15, and 45 months, respectively. Toxicity was nearly universal; cheilosis, conjunctivitis, pruritus, joint and eye pain, flashing lights, and erythrocyte sedimentation rate (ESR) over 60 were all noted. The lack of positive results and the frequency and severity of toxicity led to termination of the study.