Acute cytotoxic effects of 2-acetylaminofluorene (AAF), a powerful chemical carcinogen, were studied in cultured rat liver epithelial F258 cells. Acute treatment of these cells by AAF resulted in inhibition of cell proliferation, through an arrest in G0/G1 phase of the cell cycle, and a loss of cell viability. By contrast, AAF failed to trigger apoptosis as demonstrated by flow cytometric analysis of hypoploid sub-G1 cells. Cytochrome P4501A1 (CYP1A1), a drug metabolizing enzyme thought to play a major role in biotransformation of AAF, was induced in AAF-treated F258 cells as assessed by Northern blotting. AAF cytotoxic effects were however not blocked by the CYP1A1 inhibitor alpha-naphtoflavone, thus suggesting that they did not require CYP1A1 activity. They were also not prevented by the antioxidant N-acetylcysteine, making unlikely a major contribution of AAF-related reactive oxygen species. These data therefore indicate that AAF can exert acute cellular toxicity, including inhibition of cell growth and cell death, in rat liver epithelial cells without triggering an apoptotic process. Such an acute toxicity may contribute to the well-known promoting effects of AAF.