Summary—Twenty‐five patients with early transitional cell carcinoma of the bladder (Tis Ta T1) received intravesical instillations of 40 mg mitomycin C in 40 ml water weekly for 7 weeks. The overall response rate was 70% (complete response 40%). In patients with Ta tumours the response rate was 86%. Minor toxic side effects occurred in four patients and only one patient was unable to complete the course of treatment because of side effe