The host-mediated in vitro/in vivo assay system was used to evaluate the tumorigenic potential of the aromatic nitro compound 2-nitroanisole (2-NA). After intraperitoneal administration of the compound, resident macrophages were recovered by peritoneal lavage from treated and untreated mice and cultured in soft agar. 2-NA was shown to be carcinogenic, and the tumorigenic potential was evaluated. Additionally, by establishment of a transformed peritoneal macrophage cell line, the underlying molecular mechanism of 2-NA's carcinogenic effect was studied.