Intravesical mitomycin C therapy was administered to 63 patients with noninvasive bladder carcinoma in a phase I-II study. Doses ranged from 20 to 60 mg once a week for 8 wk. The overall response rate was 67% including a complete remission rate of 45%. The median duration of complete remission for the 2 lowest dose groups was > 14 mo., with a range of 1-36+ mo. Follow-up is not yet adequate to determine the median duration of complete remission for the higher dose groups. No bone marrow suppression or other systemic toxic effects were noted. Adverse effects were localized and occurred infrequently. No mitomycin C was detected in serial serum samples after intravesical instillation.