We studied 36 patients with stages O and A (Tis, Ta and T1) bladder cancer who had received 8 weekly doses of 30 or 40 mg. mitomycin C as definitive therapy. Of this group 16 had failed thiotepa therapy and 13 had grade III tumors (6 multifocal carcinoma in situ). The complete response rate at 12 weeks was 45 per cent (negative biopsy and cytology), while an additional 33 per cent had a partial response. Response did not correlate with tumor grade or stage. Patients who had failed thiotepa therapy were less likely to have a complete response, although the over-all response rate was identical to patients who had either not received prior chemotherapy or were not clear thiotepa failures. Followup of these patients indicates that the complete responders were benefited by this regimen since the subsequent recurrence rate was reduced when compared prior to initiation of mitomycin C. Most of these patients received monthly maintenance therapy.