To clarify the pharmacodynamics of urinary gonadotropins, same doses of Metrodin (Serono Laboratories, Aubonne, Switzerland) or Pergonal (Serono, Rome, Italy) were injected intramuscularly into normal adult men in a crossover manner, and serum follicle-stimulating hormone (FSH) and luteinizing hormone were measured by radioimmunoassay. Follicle-stimulating hormone bioavailability parameters of Metrodin (150 IU), such as peak concentration (cmax), the time when cmax is observed, half-life, and area under concentration, were 8.9 +/- 2.5 mIU/mL, 7.7 +/- 2.1 hours, 36.0 +/- 16.4 hours, and 258.6 +/- 47.9 mIU/mL X hour, respectively, and were not statistically different from those of Pergonal. On the other hand, by daily administration of Metrodin into women with isolated gonadotropin deficiency, serum FSH levels were elevated gradually, reached peak levels within 4 days, and maintained the same levels until the doses were increased. This pattern of FSH accumulation was parallel with the simulation pattern calculated using bioavailability parameters obtained from normal men, suggesting that exogenously administered FSH distributes into peripheral circulation in the manner of a one compartment model.