Lymphocyte-mediated cytotoxicity, antibody-dependent cell cytotoxicity and complement-dependent antibody assays were used to study maternal immune response to fetal antigens present on cord lymphocytes at delivery. Among 24 cell-mediated lympholysis tests, 4 were found slightly positive and accompanied by a complement-dependent antibody and/or an antibody-dependent cell cytotoxicity response. The humoral immune response was found more often positive than the cellular response.