Two open-label, randomized studies determined the bioequivalence of a test preparation (Prefest) of micronized 17 beta-estradiol (E2, CAS 50-28-2) tablets as compared with a reference preparation of micronized E2 tablets in healthy postmenopausal women. In Study 1, 36 fasting subjects received 4 test preparation 0.5-mg E2 tablets in one period and 4 reference preparation 0.5-mg E2 tablets in the other period. In Study 2, 36 fasting subjects received 1 test preparation 2-mg E2 tablet in one period and 1 reference preparation 2-mg E2 tablet in the other period. Blood samples were collected before and after dosing to determine serum concentrations of E2, estrone, and estrone sulfate. The 90% confidence intervals for the ratios of mean Cmax and AUC values (test preparation/reference preparation) for all three analytes were within the prescribed 80%-125% range of bioequivalence. In conclusion, the test preparation 0.5-mg and 2-mg micronized E2 tablets are bioequivalent to the respective strength reference preparation micronized E2 tablets.