The development of toxic edematous brain swelling in rats is accompanied by disproteinemia of the blood plasma and buildup of the gamma-globulin fraction. The administration of levopromazine (5 mg/kg), thymalin (1.2 mg/kg), or their combination reduces this disorder in the blood protein fractions. The antiedematous effect of the levopromazine--thymalin combination has an additive synergistic interaction.