Chorionic gonadotropin (CG) used at 10 and 50 IU/ml concentrations was introduced into a short-term macroculture of splenocytes of CBA mice suppressors fractionated on a nylon wool column. Regulatory effects of CG were evaluated in a syngeneic transfer system by the degree of inhibition of a humoral immune response in recipients. It was found that CG (50 IU/ml) inhibits the functional activity of splenocyte suppressors. The observed effect of the hormone was blocked by introduction into the incubation medium of the inhibitor, inositol-1-monophosphatase (lithium), and did not depend on cyclooxygenase (voltaren) or potential-independent Ca(2+)-channel (verapamil) inhibitors. Determination of the intracellular cAMP level by radioimmunoassay revealed a reliable increase of this secondary messenger in splenocyte suppressors during their incubation with CG. The ability of CG (50 IU/ml) to inhibit the functional activity of intact T-lymphocytes (but not B-cells) was established. The suppressive hormone activity was also followed by cAMP level increase in target cells. These findings suggest that the mechanism of a transmembrane transfer of the CG signal in splenocyte suppressors is related to the adenylate cyclase system and, probably, to phosphoinositide metabolism products.