l7α-hydroxyprogesterone (up to 200 µg/day) and 11β-hydroxyandrostenedione (up to 500 µg) had n effect on PMS-induced ovulation in intact immature rats. 10 µg/day of testosterone propionate (TP) on days 28–30 of life decreased the percent of animals ovulating and the number of ova produced; this effect persisted in adrenalectomized animals with or without corticosterone replacement. Three daily doses of 10 µg TP increased the electrical threshold of the medial preoptic area in pentobarbital-blocked, PMS-stimulated animals. And TP decreased the rate of release and synthesis of FSH during the ovulatory surge, and the storage and rate of release of LH; it also inhibited the response to HCG in the PMS-primed animal, suggesting a direct target-organ