During long periods of buffered instillations of mitomycin C (MMC) and doxorubicin (adriamycin; ADM) on carcinoma in situ (TIS), the complete response was 82% for MMC and 80% for ADM. Even the frequency of progression was about the same (20% in both groups). The differentiation grade was shown to be of great prognostic value. No progression occurred in grade 1 and 2 contrary to 38% in grade 3 cancers. The cytological primary diagnosis of TIS was equally able to predict the prognosis as the histological verification. An interesting phenomenon was the fluctuation to the cytological picture during the treatment. The change of instillation drug might be useful in cases of stable disease, though not in chemical cystitis. The addition of methylprednisolone can relieve bladder irritation.