The cytostatic agent TS160 inhibited DNA synthesis in V79 cells while the course of RNA synthesis and protein synthesis were not changed significantly. DNA inhibition was in direct correlation with the inhibition of growth and reduction of colony-forming ability in the treated cells. The study of the mutagenic consequences of single or repeated TS160 treatments showed that TS160 had a significant mutagenic activity on Chinese hamster V79 cells. In the study of mutagenic effects of TS160, we used the method of repeated treatment of surviving cell fractions with this compound. This method is suitable for those mutagens (e.g. weak mutagens) whose mutagenic activity on mammalian cells in vitro might escape attention after application of a single dose. The possible causes of mutagenic effects of TS160 are discussed.