This study was undertaken to assess the value of intravesical interferon alfa-2b treatment in preventing the recurrences of superficial transitional cell carcinoma of the bladder. A total of 30 patients aged from 33 to 78 entered the protocol. The intravesical instillations were performed once a week for 8 weeks. A solution of 10 X 10^6 IU interferon alfa-2b in 30 ml of normal saline was used. Follow-up ranged from 12 to 28 months. Of the 30 patients, 19 (63.33%) were tumor free at the end of follow-up. Of the remaining 11 patients, 7 presented with recurrent superficial tumors and 4 with invasive bladder tumors. No side effects were noted.