In adult women, estradiol (E2) sensitizes the pituitary to GnRH. To assess whether this effect develops during intrauterine life, dispersed pituitary cells from second trimester male and female fetuses were cultured on extracellular matrix-coated plates. E2 (10(-8) mol/L) exposure for 72 h resulted in a significant increase in LH release when cells were stimulated with GnRH and caused a significant shift to the left of the dose-response curve for GnRH-stimulated LH release [relative potency ratio, 0.33 +/- 0.05 (+/- SE)]. E2-enhanced LH release was not associated with an increase in cell number, total LH content, or percentage of LH-containing cells (immunocytochemistry). The EC50 of GnRH-stimulated LH release and the degree of E2 sensitization were not sex dependent, although female fetal pituitary cells in the absence of E2 had significantly greater LH content and released more LH under basal and GnRH-stimulated conditions than cells from male fetuses. Therefore, E2 sensitization of second trimester human fetal gonadotrophs to GnRH does occur, is not influenced by sex, and may involve an acutely releasable LH pool. At these gestational ages, basal and maximal GnRH-stimulated LH release as well as total LH content are greater in the female than the male. Thus, E2 sensitization of GnRH responsiveness appears to have its origins during intrauterine fetal life.