Results of study of the cytotoxic effect of the lymphotoxin on the monolayer culture of the peritoneal macrophages used as target cells are presented. The lymphotoxin was obtained following an 18-hour incubation of the lymph node cells of guinea pigs with delayed hypersensitivity to tuberculoproteins, in the presence of the specific antigen (tuberculin). It was shown that only on the 5th--6th day of cultivation did the supernatants destroy more than half of the macrophages in 70% of the experiments. The death of the macrophages during the later periods of cultivation, in comparing with the L-cells, suggests a different resistance of these target-cells to the cytotoxic effect of the lymphotoxin.