The effect of estrogen and progestin on pituitary responsiveness to 150 mug synthetic luteinizing hormone-releasing factor (LRF) was assessed in premenopausal women receiving sequential (n=12) and combination (n=7) contraceptive steroids. A marked contrast in the time-course and maximal response to LRF was found; a prompt but quantitatively smaller luteinizing hormone (LH) response was seen during cyclic combination therapy, while a delayed (five times) but enhanced (fivefold) LH response was observed during estrogen segments of cyclic sequential therapy. For follicle-stimulating hormone (FSH), the maximum rise was also higher, and the peak response was similarly delayed in the latter group. The quantitative secretion in response to LRF for LH (area under the curve), but not for FSH, was significantly greater (P < 0.01) in subjects receiving sequential, as compared to subjects receiving combination treatment. In both groups, characteristic gonadotropin responses to LRF were reproducible and were independent of the duration of treatment. Since LRF studies were performed during the estrogen segment of treatment cycle in subjects receiving sequential steroids, our data suggest that estrogen exerts a direct feedback action at the pituitary level and that pituitary responsiveness to LRF is augmented by estrogen.