OBJECTIVE: To establish the feasibility of anti-fertility by ultraphysiological-dosage testosterone in male. METHODS: Ten healthy, fertile men received 200 mg testosterone enanthate weekly by intramuscular injection based on international standard protocol. RESULTS: After 3-month injection, severe oligospermia was achieved. After 6-month injection, azoospermia was achieved. The total consecutive administration lasted for 12 months. During the period of severe oligospermia and azoospermia no partner was pregnant. After stopping injection, the sperm output returned to normal (20 x 10(8)/ml) in 2-3 months up to individual's own level before administration in 6 months. CONCLUSION: Severe oligospermia and azoospermia can be induced by ultra-pathological-dosage tesosterone through inhibiting FSH, LH to cause spermatogenesis inhibition. The sperm output would recover to its previous level in 6 months after stopping injection. It is suggested that there is a strong possibility that high-dosage testosterone may act as a male contraceptive.