Thirty-five patients (33 males, median age 58) with stage T alpha (21 patients) or T1, grade 1 (17 patients) or grade 2 superficial bladder carcinoma, were treated with transurethral resection (TUR) followed by intravesical prophylactic therapy with 10 mg mitoxantrone administered weekly for 6 weeks and then monthly for 10 months. Twenty-five patients were newly diagnosed and 10 had relapsed after previous therapy. Diagnosis was confirmed with cytology and biopsy. The aim of the study was to evaluate the prophylactic effect (relapse rate, disease free interval) and toxicity of intravesical mitoxantrone in superficial bladder carcinoma. Relapses were established with biopsy. After a mean period of 12 months follow-up (median 8.3 months), 63% of patients in the whole group, 72% in the newly diagnosed group and 40% in the group of previously relapsed patients remained relapse free. These rates compare very favorably with the most effective prophylactic agents available. At the end of the follow-up period the median disease-free survival for the whole group was not reached. Therapy was well tolerated with no systemic toxicity and 14 patients reporting grade 1-2 local toxicity. In no patient was treatment discontinued due to toxicity. Mitoxantrone is an effective and safe agent for the post-TUR adjuvant intravesical therapy.