A method for the separation and quantitative determination of epimeric 3alpha/beta-hydroxy-5alpha/beta-pregnan-20-ones by gas liquid chromatography and electron capture detection is presented. Reliability of the method and applicability to biological material was tested. In one total human uterus and 20 samples of myometrium the concentration of epimeric pregnanol-ones was determined. 3beta-hydroxy-5alpha-pregnan-20-one and 3alpha-hydroxy-5alpha-pregnan-20-one were present in similar quantitative range as progesterone and 20alpha-hydroxy-4-pregnen-3-one. A correlation between progesterone and concentration of metabolites could not be established. 3beta-hydroxy-5beta-pregnan-20-one was not detected in the tissue.