Six subjects aged between 19 and 29 years were studied. Gonadotrophins, follicular stimulating hormone or FSH and luteotrophic hormone or LH, were low in all cases. Under the influence of a single dose of 150 microgram of hypothalamic gonadotrophin liberation factor (LHRH), there was a preferential increase in FSH whilst levels of LH were little influenced. The continuous infusion of LHRH was associated with the same phenomenon. Only prolonged administration (for approximately 12 months) of chorionic gonadotrophins, resultes in a significant rise in plasma testosterone levels (low in all cases in the absence of stimulation). The level of urinary 3alpha-androstanediol represents a good parameter of androgenicity. Urinary 3beta-androstanediol is a metabolite of androgens formed in the liver. In hypogonadotrophic hypogonadism, and in particular in de Morsier's syndrome, the essential element would seem to be the absence of solicitation of the pituitary gonadotrophic cells by virtue of inadequate secretion of LHRH. The results of stimulation with chorionic gonadotrophins reflects the existence of inadequate maturation of testicular receptors to these hormones.