Interferon (IFN) was used in the treatment of superficial bladder tumors. Interferon (IFN-beta, IFN-gamma) was instilled into the bladder at dosages ranging from 16 billion to 36 billion U IFN per 30 ml physiological saline. The IFN was instilled into the bladder once a day or twice a day for 10 to 20 days. In this trial, ten patients with superficial bladder tumors were treated at Okayama City Hospital, and of these, 1 CR, 3 PR, 2 MR and 4 NC were obtained. There were no signs of either irritable bladder or general side effects. IFN (especially IFN-beta) is considered a useful drug for superficial bladder tumors in intravesical chemotherapy.