Various cancer chemotherapeutic agents were examined for their ability to produce increases in sister chromatid exchanges in hamster A(T1)Cl-3 cells. Those agents which produce oncogenic transformation and chromosomal breaks also showed significant increases in sister chromatid exchanges. Those drugs are not oncogenic or clastogenic in cell culture produced no increases in sister chromatid exchanges. In general, concentrations which yielded increases in sister chromatid exchanges were considerably lower than those which produce oncogenic transformation and chromosomal breakage. This was particularly true for the alkylating agents. Examining increases in the production of sister chromatid exchanges may be an additional, sensitive method for detecting potential mutagenic and/or oncogenic agents in the environment.