The complexes of the estrogen alpha-receptor with estradiol and 8-isoestradiol were comparatively analyzed. The computations of ligand-receptor complexes, carried out using the FLEXX program, allowed us to propose a model for the binding of the analogues of 8-isoestradiol. It was found that rings C and D of estradiol and 8-isoestradiol are similarly arranged in the ligand-binding pocket and coincide upon the superposition of the corresponding ligand-receptor complexes, whereas rings A and B do not coincide. The oxygen functions in position 17 of the estradiol analogues of both series coincide upon superposition, whereas the phenol 3-hydroxyl groups are 0.05 A apart. A comparison of the predicted biological properties of modified estradiol analogues of the natural and 8-isoseries with the available experimental data revealed their similarity. Synthetic 2-acetyl analogues of 8-isoestrogens were found to have no uterotropic activity, which is also consistent with the proposed model.