Biological activity of disulfated polyhydroxysteroids from the Pacific brittle star Ophiopholis aculeata. The action of (20R)-cholesta-5,25-diene-3 alpha, 4 beta, 21-triol 3,21-disulfate and its 25,26-dihydroanalog from the Pacific brittle star Ophiopholis aculeata was studied on mouse cancer cells, lymphocytes and erythrocytes. The cytotoxic and hemolytic effects were not observed for both steroids at the wide range of concentrations. Both steroids inhibited 3H-Thymidine (but not 3H-Uridine) incorporation into Ehrlich carcinoma cells. It was the first time shown that some sulfated marine polyhydroxylated steroids stimulate the influx of Ca2+ into cells. (20R)-Cholesta-5,25-diene-3 alpha, 4 beta, 21-triol 3,21-disulfate was two times more active than its 25,26-dihydro-analog.