Between 1980 and 1984, 44 patients were treated for bladder cancer by preoperative irradiation of 40 Gy to the pelvic region followed by total cystectomy. These patients were prospectively divided into two groups at random. In 23 cases, 500 mg of misonidazole (MISO) was administered four hours prior to irradiation. Twenty-one patients were preoperatively treated by radiation alone. Most patients had histopathological grading of G3-4, and the distribution of T-factors in the two groups was comparable. Thirty-seven patients out of 44 underwent total cystectomy within three weeks after irradiation. pT-factors were carefully examined in resected specimens. Survival rates were calculated by the Kaplan-Meier method. The 5 year survival rate for T3 patients in the group treated by MISO combined with radiotherapy was 59%, while that for T3 patients in the radiation only group was 43%. A reduction in T-factors was observed in 9 of 17 T3 cases treated by MISO combined with radiation, and in one of 14 T3 cases treated by radiation alone. This finding was significant on chi-square test (p = 0.02). Since the survival rate of T3 patients with a reduction in T-factors by preoperative irradiation was superior to that of cases without reduction (70% vs. 43%), the combined use of MISO in preoperative irradiation seems to be useful for the treatment of T3 bladder cancer.