Experiments with cultured Chinese hamster cells showed that incubation of the cells with (phosphatidylcholine + cholesterol + 7-ketocholesterol)-containing liposomes (4:3:1 by weight) during two hours led to a decrease in the colony-forming ability of cells down to zero, while (phosphatidylcholine + cholesterol)-containing liposomes (1:1 by weight) reduce this parameter by 90%. Furthermore, the cholesterol-containing liposomes (without 7-ketocholesterol) induce a decrease in the number of the maximal-site colonies accompanied by the corresponding increase in the number of the middle-size colonies.