Forty-three patients with recurrent multiple superficial bladder tumours (Tis, Ta and Tl) were treated with Mitomycin C 20 mg in 20 ml water intravesically weekly for 8 to 12 weeks, and monthly instillations were continued for 5 to 6 months. Residual tumour was resected at 12 weeks, at which time 40 patients (93%) showed a response to treatment. A complete response was seen in 24 (56%) and 16 (37%) showed a partial response. After a follow-up of 12 to 48 months (median 19), 19 of 33 evaluable patients (58%) have shown tumour recurrence. Invasive tumour has developed in seven (17%) and transitional cell tumours of the ureter in two of those patients who showed an initial response to treatment.