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ExtractLuteinizing hormone-releasing hormone (LH-RH), purified from porcine hypothalamic tissue, was administered in an intravenous dose of 300 /xg to four prepubertal and four adult human subjects. The resulting increases in plasma levels of LH and FSH were statistically significant (P < 0.01) in the 16-and 32-min samples, but did not differ with the age or sex of the subject groups. The mean maximum increase in plasma LH values was 290% for men and 425% for women. Injection of LH-RH resulted in a 500% mean maximum increase in LH levels in the plasma of boys and 850% in that of girls. The gonadotropin release induced by injection of LH-RH was sufficient to increase plasma levels of estradiol in some individuals. No significant elevation occurred in the levels in plasma of growth hormone, thyrotropin, or cortisol. It is concluded that LH-RH is a potent and specific hypothalamic releasing hormone for LH and FSH in prepubertal children as well as in normal adults. SpeculationThe increases in gonadotropin levels in plasma of all groups seem to reduce the possibility that a change in pituitary responsiveness to LH-RH occurs at puberty. However, similar studies involving larger numbers of individuals tested at varying doses might reveal differences in responses to LH-RH between age or sex groups.