Objective: We sought to determine the optimum estradiol valerate–medroxyprogesterone acetate regimens for efficacy and safety. Study Design: We performed a 24-month, randomized, double-blind phase II study. Four hundred nineteen women who were postmenopausal for at least 3 years were placed in six parallel treatment groups and received 1 or 2 mg estradiol valerate with either 2.5 or 5 mg medroxyprogesterone acetate. In two groups the dose of estradiol valerate was increased from 1 to 2 mg estradiol valerate after 6 months. Results: A marked improvement of climacteric symptoms was observed, and most women had no bleeding even during the first 3 months of treatment. The best bleeding pattern was achieved with 1 mg estradiol valerate and 2.5 or 5 mg medroxyprogesterone acetate, and in most groups the bleeding pattern improved over time. No cases of hyperplasia were observed. Conclusion: All regimens alleviated climacteric symptoms and provided excellent bleeding control, even during the early weeks of treatment. A choice of various dose combinations offers flexibility of dosing, thus enabling therapy to be tailored to the needs of individual women. (Am J Obstet Gynecol 2000;182:560-7.)