The aim of this study was to demonstrate whether development of the humoral or cellular immunity to sheep erythrocytes (SRBC) can be inhibited by a transfer of antigen-specific CD4+ T cells isolated from mice exhibiting cellular or humoral response. For generation of the humoral immune response and suppressor T cells for the cellular immunity, mice were immunized with a high dose of SRBC intraperitoneally (i.p.). On the other hand, for development of the cellular response and generation of T cells with inhibitory activity in relation to the humoral response, mice were immunized subcutaneously (s.c.) with SRBC emulsified with complete Freund's adjuvant or intravenously (i.v.) with low dose of SRBC (10(5)). We showed that depletion of CD4+ but not CD8+ T cells in the populations of transferred T cells abolished their inhibitory activity. The phenomenon of this suppression was dependent on a dose of T cells transferred and was antigen-specific, since T cells specific for chicken erythrocytes did not inhibit anti SRBC-response. The data indicate the importance of antigen specific CD4+ T cells in the mutual regulation of the two major type of the immune response.