3-Chloro-p-toluidine hydrochloride (CPT-HCI) is an aniline derivative used in the manufacture of the dye palatine fast yellow; it is also registered as a selective, low-volume-use (<45 kg/yr) avicide. Three in vitro mutagenicity tests of CPT-HCI were performed according to methods recommended by the U.S. Environmental Protection Agency (EPA): the Ames/Salmonella assay, the Chinese hamster ovary/hypoxanthine-guanine phosphoribosyl-transferase (CHO/HPRT) mammalian cell forward gene mutation assay, and the CHO chromosome aberration assay. CPT-HCI did not display mutagenic activity using the /4mesAalmonella or CHO/HPRT assays. However, CPT-HCI induced statistically significant, concentration-dependent, metabolically activated increases in the proportion of aberrant cells and aberrations/cell in cultured CHO cells. Results are suggestive of minimal mutagenicity effects associated with exposure to anilines and their derivatives.