Patients with pathologically defined prostatic carcinoma (114 cases in 23 institutes) were subcutaneously administered 500 micrograms of Buserelin (Hoe 766) 3 times a day for 7 consecutive days, then randomized to intranasally administered 600 or 900 micrograms/day of Buserelin as maintenance treatment. We examined the clinical efficacy, safety and endocrinological effects of the drug by the intranasal dosage. Size of prostate decreased more than 25% in 21 cases (total 47 cases; measured at the start and 3 months treatment by ultrasonography. Complete response and partial response were observed in 13 cases (16.1%) by NPCP's criteria at 3 months Buserelin treatment. Grobal Improvement Rating (GIR) were respectively 64.3% (600 micrograms group) and 68.0% (900 micrograms group). Grobal Utility Rating (GUR) were respectively 85.7% (600 micrograms group) and 82.0% (900 micrograms group). No significance was observed in these two groups. Adverse reactions were observed in 21 cases (18.9%). Except in 1 case, they were slight and the Buserelin treatment could be continued. Objectively Safety Rating (OSR) was 92.8%. Five cases were treated for more than 2 years with Buserelin and these cases were well controlled. Buserelin was considered as an effective and safe drug to treat prostatic carcinoma.