Peripheral plasma from four postmenopausal women was analysed for estrone, estradiol, lutenizing hormone and follicle stimulating hormone during 24 hours following an oral intake of a single dose of 1.0 mg micronized estradiol, on the first day of therapy and after one month. A similar study was carried out with another four postmenopausal patients, who received 0.2 mg estradiol three times daily. The measurements were performed by radioimmunoassay (RIA). It is concluded that the plasma concentrations of estrone and estradiol are higher and those of FSH lower after one month of therapy than on the first treatment day, while plasma LH remains unchanged. Micronized estradiol is rapidly absorbed from the gastrointestinal tract and converted to estrone, and the plasma profiles of estrone during the day are more constant with a divided daily dose than with a single higher dose. The divided daily dose results in an equally good clinical effect even though the total administration of estradiol is lower.