Esterified 19-nortestosterone, an anabolic steroid which has been in clinical use for over 20 years, was administered intramuscularly to five healthy volunteers in doses of 100 mg/week for 3 weeks followed by 200 mg/week for a further 10 weeks. Azoospermia occurred 7 to 13 weeks after initiation of treatment and persisted for 4-14 weeks after the last injection. Serum gonadotropin and testosterone levels were reduced, but androgenic effects were maintained as indicated by unchanged libido and potency. No serious side-effects were noted. 19-nortestosterone appears to be a potential agent for male fertility control.