In a two-way crossover study in 18 young female volunteers aged from 22 to 38 years the relative bioavailability and pharmacokinetics of esterified estrogens were investigated after single administration of a sugar-coated tablet formulation (Femavit 1.25) in comparison to a single dose of an oral suspension. The content of active ingredients was in both cases 1.25 mg esterified estrogens. As marker compound the dominating active compound estrone (CAS 53-16-7) was chosen. Estrone in serum was measured using a validated radioimmuno assay. The administration of the test and reference preparation was performed on either day 3-7 of two subsequent menstruation cycles in order to obtain low endogenous hormone levels. The relative bioavailability of estrone from the test preparation, based on the total AUC (AUC under the baseline + AUC over the baseline), was 99.2% (90%-confidence interval 91.8-107.1%) und therefore fulfilled the bioequivalence criterion. After deduction of the baseline-AUC a relative bioavailability of the sugar-coated formulation of 113.9% was found, with a broad 90% confidence interval of 72.5-178.9%, due to a higher variability. The absolute Cmax values were similar (255 pg/ml after tablet administration and 279 pg/ml after suspension), bioequivalence also in regard to Cmax was proven. The value of tmax was 4 h for both preparations.