Twenty-five patients with Ta-T1 transitional cell carcinoma of the bladder were treated by transurethral resection (TUR) followed by intravesical chemoprophylaxis with mitoxantrone (10 mg diluted in 50 ml normal saline) administered weekly for 6 weeks. After a mean follow-up of 12 months, 76% of patients in the whole group, 69% in the newly diagnosed patients and 89% in the group of previously relapsed patients remained relapse free. These rates compare favorably with the other prophylactic agents available. Therapy was well tolerated in most patients, with only two patients reporting grade 3 local toxicity. We conclude that mitoxantrone is an effective and safe agent for intravesical chemotherapy.