Meningiomas were removed from four patients and estradiol binding was measured in the tumor tissue. Cell cultures were established and an in vitro system was developed to test the biological activity of physiologically relevant concentrations (10(-7) M and 10(-9) M) of estradiol-17 beta, progesterone, and the anti-estrogen, tamoxifen, on the growth of meningioma cells in early culture (passages 3 to 5). Assays of the frozen surgical specimens demonstrated cytosolic estradiol binding, with levels of 0.3 to 26.7 femtomoles (fM)/mg protein, in all four tumors. Nuclear estradiol binding was detected in three tumors, with levels of 16.8 to 39.5 fM/mg protein. In cell culture, estradiol at either 10(-7) M or 10(-9) M consistently stimulated cell growth in all four cultures. When tested alone, progesterone stimulated the growth of all four tumors and tamoxifen stimulated the growth of three of the four tumors, but the levels of stimulation produced by either of these compounds were less pronounced than the level produced by estradiol. When tested in combination with estradiol, progesterone significantly inhibited the growth stimulation produced by estradiol in all four meningioma cultures and tamoxifen significantly inhibited estradiol-induced growth stimulation in three of four cultures. It is not known if these effects are mediated by a hormone receptor or by a hormone binder different from a true receptor, or if they are caused by alterations in cellular metabolism that are independent of specific hormone binding. However, the authors conclude that this in vitro technique can be used to further study the biological activity of hormones on human meningiomas in order to answer these questions.