To investigate the transforming potency of flavoring agents, Chinese hamster (CH) B241 cells were treated with various concentrations of flavoring agents for 24 hours during their exponential growth period. Surviving cells were cultivated for generations without the agents to observe the appearance of growth properties characteristic of transformed cells. Highly increased rates of structural and numerical chromosome abnormalities were seen in the cells treated with a high concentration of the agents, especially with allylisothiocyanate (AITC) or tr-cinnamic aldehyde (CA). During subsequent passages of the treated cells, the survivors from treatment with sublethal doses of AITC or CA showed a significant increase in cloning efficiency in soft agar medium, especially after passage in soft agar. Also noted was an increase in saturation density in monolayer culture, though a significant increase in plating efficiency at low serum level was not observed. These characteristic changes in AITC- or CA-treated cells were associated with the significant increase in frequencies of cells containing almost 3n to 4n chromosomes.