Stimulatory therapy with either GnRH or gonadotropins is an effective treatment to induce spermatogenesis and achieve paternity in men with secondary hypogonadism. However, there is still uncertainty about the optimal treatment modality and schedule, the duration of treatment necessary and the influence of interfering factors such as maldescended testes. We have extended our previous series of men treated for secondary hypogonadism and now present our therapeutic experience with 42 cases. Twenty-one patients with hypothalamic disorders (11 with idiopathic hypogonadotropic hypogonadism (IHH) and 10 with Kallmann syndrome (KalS)) were treated with GnRH (group Ia) or human chorionic gonadotropin (hCG)/human menopausal gonadotropin (hMG) (group Ib), and 21 patients with hypopituitarism (group II) were treated with hCG/hMG. A total of 5 7 treatment courses were initiated for induction of spermatogenesis, 36 of these for the purpose of induction of pregnancy in the female partner. Bilateral testicular volumes doubled within 5-12 months of therapy. Spermatogenesis as evidenced by the appearance of sperm in the ejaculate was induced in 54/57 courses. Pregnancies occurred in 26/36 courses. Unilaterally maldescended testes did not preclude patients with IHH or KalS from gaining fertility under therapy and spermatogenesis could be successfully initiated even in some individuals with bilateral maldescended testes. In general there was a tendency for a longer duration of therapy until induction of spermatogenesis in patients with a history of bilateral cryptorchidism. However, this did not reach statistical significance. In patients with IHH or KalS treated with either hCG/hMG or GnRH there were no statistically significant differences in terms of duration to appearance of sperm or pregnancy rates. Even in KalS patients as old as 43 years spermatogenesis could be induced. In repeatedly treated patients stimulation of spermatogenesis tended to be faster while time until induction of pregnancy was significantly shorter in the second treatment course. In conclusion, GnRH or hCG/hMG are effective therapeutic modalities for patients with IHH or KalS. It remains to be determined whether highly purified urinary gonadotropin preparations or recombinant LH and FSH will provide therapeutic advantages.