The effect of 10(3)-10(5) E/20 g doses of the recombinant factor of human beta tumor necrosis (rFNT-beta) on formation of the immune response and macrophage functional activity was studied in CBA and C57Bl/6 mice that differ in genetically determined level of the immune response to an antigen (sheep erythrocytes). The rFNT-beta was found to cause a modulating effect on the cell and humoral links of the immune response. The effect of the agent depended on the dose and the genotype of the experimental animals. It is suggested that the interlinear differences in the intensity of the humoral immune response in rFNT-beta administration may be connected with the different sensitivity to the agent of the peritoneal macrophages of mice of the used lines.