We studied the serum estradiol and estrone levels in 146 peri and postmenopausal women, and in 38 women who had complained of various climacteric disturbance symptoms during daily hormone replacement therapy (HRT) with conjugated equine estrogen (CEE) 0.625 mg and medroxyprogesterone acetate (MPA) 2.5 mg. Serum estradiol and estrone were measured before treatment, and at 6 months, and after one year of the HRT therapy by HPLC-radioimmunoassay. In 146 peri and postmenopausal women, the serum level of estradiol was from 3 to 6pg/ml. The serum level of estradiol in 38 women after HRT significantly increased (p < 0.01) from 3.34 to 23.6 pg/ml at 6 months, and 21.5 pg/ml at 12 months. The serum level of estrone significantly increased (p < 0.01) from 26.6pg/ml to 156.7pg/ml at 6 months, and 137.2pg/ml at 12 month. These results are very useful for deciding on the doses of hormones and the expected serum estradiol level in HRT for Japanese women.