24 patients with recurrent (group 1) or primary (group 2) bladder cancer (ta/t1 G2) were given 50.000.000 U.I. of beta interferon intravesically after TUR of the neoplasm. In group 1 recurrence rate (rr) was 100% in the period before INF and 83% after INF treatment (follow-up 15-24 months, median 19.8) (p = ns). In group 2 rr was 25% in a 24 months, median 19.8) (p = ns). In group 2 rr was 25% in a 24 months follow-up period; if compared to the rr of a historical control group treated by only a TUR (38.2%) there was a statistically significant difference (p less than 0.01). Tolerability of the drug was excellent.