Estrogens are supposed to be responsible for the increased sensitivity of the pituitary to LHRH and TRH observed in female in comparison to male adults. The influence of physiological and pharmacological variations of estrogens was studied throughout female life. Adolescents girls showed enhanced responses to both LHRH and TRH, as compared to cycling adult women. The adolescent pituitary seems to be particularly sensitive to the increasing estradiol secretion. Adult cycling women disclosed higher LH and FSH responses to LHRH during the periovulatory and luteal phases than during the follicular phase; prolactin response to TRH was enhanced only during the periovulatory phase while TSH response remained constant throughout the menstrual cycle. In adult women, sequential oral contraceptives increased LH, FSH and prolactin responses to LHRH and TRH while TSH response was unchanged. Combined contraceptives displayed an important inhibition of the LH, FSH and TSH responses but not of that of prolactin. The inhibitory effects on gonadotrophins and TSH may be due to the association of gestagens to estrogens. Postmenopausal women presented a TSH response to TRH similar to that found in male adults while prolactin response remained unchanged in spite of decreased basal values. The potentiatory effects of estrogens on the pituitary responsiveness to LHRH and TSH may be attributed either to an increased number or to an enhanced binding activity of the pituitary receptors to LHRH and TRH, as suggested by several experimental data.