The effects of gonadotrophin administration to 17 Chinese patients with hypogonadotrophic hypogonadism (HH) on testicular volume and induction of spermatogenesis were studied. Ten subjects had isolated HH and seven had hypopituitarism. Twelve of the subjects had prepubertal onset of HH and five of them had been treated previously with hCG for induction of puberty. None had a history of cryptorchidism. During hCG treatment for induction of spermatogenesis, all subjects had an increase in serum levels of testosterone into the normal adult male range and their testes increased in size from 3 (1-20) ml to 11.6 (5-20) ml [median(range), p < 0.02]. Six subjects required treatment with hCG alone. However, the remaining 11 subjects, after at least 6 months treatment with hCG, required the addition of human menopausal gonadotrophin (hMG) to induce spermatogenesis. Two subjects remained azoospermic. One had a history of mumps orchitis and the other had isolated elevation of blood FSH levels, suggestive of primary testicular failure in addition to HH. Excluding one subject with fertile eunuch syndrome, the mean duration for first appearance of spermatozoa was 13 (4-52) months. Twelve subjects became fertile and pregnancy was achieved in their partners after 20 (4-78) months. The weekly doses for hCG and hMG were 4000 (3000-10,000) IU and 225 (225-450) IU, respectively. Patients who responded to hCG alone had a significantly larger pretreatment testicular volume, suggesting that they had only partial gonadotrophin deficiency. Prepubertal onset of hypogonadism was not a determining factor for requirement of hMG treatment.(ABSTRACT TRUNCATED AT 250 WORDS)