The radioisotopic method with the use of immunosorbents was applied to the study of the synthesis of antibodies and nonspecific immunoglobulins in the mono- and mixed cultures of cells of the immune lymph nodes and intact bone marrow in removal of the adherent or T-cells. Treatment of the lymph node cell population with anti-O-serum decreased the antibody synthesis to 30%, whereas removal of the adherent cells - to 70%. In combined cultivation of the cells of immune lymph nodes, devoid of adherent cells, with the intact bone marrow cells the effect of stimulation of immunoglobulin synthesis was not eliminated, whereas treatment of cells of the immune lymph nodes with anti-O-serum doubled this effect. Possible mechanisms of the effect of stimulation of the immunoglobulin synthesis in mixed culture is discussed, and a conclusion was drawn on the necessity of cooperation between the individual types of cells during the productive phase of the immune response.