Аннотация:A method of quantitative determination of the areas of binding of a peculiar estrogen-binding protein (PEBP) in the cytosol of the rat liver by means of ion-exchange sorption on DEAE-cellulose is suggested. For differential determination of the PEBP contribution to the total estradiol (E2) binding with cytosol proteins a unique capacity of PEBP to form complexes with 3H-E2, which were rapidly decomposed on addition of an excess of unlabeled E2, was used. Theoretical prerequisites and experimental substantiation of the suggested method of the PEBP testing are considered. The content of the binding PEBP areas in the cytosol of the liver of male rats, measured by the mentioned method, constituted (5.8 +/- 0.7).10(-12) mol per 1 mg of protein (M +/- m, according to the data of 18 determinations). No analogous areas of E2 binding were revealed in the cytosol of the liver in female rats. It was also demonstrated that the cytosol of the liver of male rats contained specific areas of testosterone (T) binding, forming highly labile complexes with 3H-T, rapidly decomposing in the presence of an excess of T and E2.