A double-blind crossover study was designed to compare the effects of placebo and medroxyprogesterone acetate, 20 mg, on vasomotor flushes and blood hormones in 27 postmenopausal women. In women receiving placebo, vasomotor flushes were decreased by 25.9% during the last four weeks of treatment compared with baseline, and a further decrease of 34.5% was achieved by the last four weeks after patients were given medroxyprogesterone. In women who initially took medroxyprogesterone, there a 73.9% decline by the last four weeks in the number of vasomotor flushes. However, when these women were given placebo, an immediate worsening of their symptoms occurred. The drug produced a decline of 27% and 29% in serum levels of follicle-stimulating hormone and luteinizing hormone, respectively, while the serum prolactin level rose slightly. Thus, medroxyprogesterone can be used to treat the vasomotor flushes of postmenopausal women when estrogen use is undesirable.