Prolonged intermittent treatment with low doses of GnRH was given to a 23-yr-old man with secondary hypogonadotropic hypogonadism. The patient had experienced sudden onset of diabetes insipidus followed by progressive decrease of gonadotropins and gonadal function. Modern radiological techniques did not reveal any organic genesis. A small portable computerized infusion pump connected to a sc catheter was used for the 220-day GnRH therapy. One microgram gnRH was administered every 90 min during the first 90 days and 5 micrograms GnRH every 90 min during the following 130 days. During the prolonged GnRH treatment testosterone secretion normalized, libido and potency improved, and ejaculation returned. Spermatogenesis became close to normal and the subject's wife became pregnant after 181 days of treatment. The prolonged treatment with the small infusion pump was well accepted and did not interfere with the patient's daily life activations. Thus, chronic pulsatile low dose GnRH treatment can restore normal pituitary-gonadal function in idiopathic male hypogonadotropic hypogonadism.