A study was made of the effect of the drugs with an immunostimulant (T-activin, levamisole) and immunosuppressant (prospidin) activity on the synthesis of IgA, IgM and IgG in vitro in lymphoid cultures of 7 healthy donors, 16 patients with seropositive and 9 patients with seronegative rheumatoid arthritis (RA). It was shown that the model of the synthesis of immunoglobulins in vitro demonstrates the impairment of T-B-cell cooperation of lymphocytes in RA patients. It was establised that the effect of immunologically active drugs on the synthesis of immunoglobulins depends on the character of the drug immunotropic action and initial functional activity of the immunoregulatory T-lymphocytes. Like polyclonal mitogens, levamisole and, to a greater extent, T-activin stimulating the initially low activity of T helpers increase spontaneous synthesis of immunoglobulins in lymphoid cultures of patients with seronegative RA, whereas in seropositive RA, these drugs stimulating the initially low activity of T suppressors carrying Fc gamma-receptors inhibit this process. Prospidin inhibit the synthesis of immunoglobulins equally in both RA patterns. Indications and contraindications for administration of he immunologically active drugs on a clinical bases are discussed.