A bioavailability study was performed on ten oophorectomized women in a randomized cross-over design. The absorption of tablets containing 2 mg of micronized oestradiol and 1 mg of micronized oestriol (Estrofem) was compared to the absorption of the same micronized hormones administered in an aqueous suspension. Serum concentration values of oestradiol, oestriol and oestrone were measured by radioimmunoassay. The data obtained were analyzed both by univariate and multivariate analyses, and neither the serum concentrations at the various sample times, the maximum concentrations, the times for the maximum concentrations, nor the areas under the serum concentration curves disclosed any significant differences between the tablet and suspension administrations at the 5% level. The serum concentration values achieved by giving 2 mg of oestradiol and 1 mg of oestriol were of the same magnitude or higher than those of the normal menstrual cycle.