The mitotic index of hepatocytes remained unchanged after 10 intraperitoneal injections of DSLET and ACTH(4-10) in doses of 0.5, 1.5, and 5 microg/kg, but increased after injection of these substances in doses of 50 and 150 microg/kg. DSLET in doses of 5, 50, and 150 microg/kg decreased the number of antibody-producing cells in the spleen. ACTH(4-10) possessed immunosuppressive activity not only in these doses, but also in a dose of 1.5 microg/kg. As differentiated from mitotic activity of hepatocytes, the degree of immunosuppression increased with increasing the dose of test peptides.