Lung cancer is the leading cause of cancer deaths worldwide. Epidemiological studies have shown that exposure to cooking oil fumes (COF) is a risk factor for lung cancer. Trans, trans-2,4-decadienal (tt-DDE), a dienaldehyde, is abundant in heated oils and COF. Previously, we found that long-term exposure (45 days) to a sub-lethal dose (1 microM) of tt-DDE significantly increased growth of human bronchial epithelial cells (BEAS-2B). Aims of this study are to understand the mechanism of tt-DDE-induced cell proliferation and possible protective effects of antioxidant, vitamin C and N-acetylcysteine (NAC) in BEAS-2B cells. Utilizing the real-time RT-PCR and Western immunoblotting, we found that p27 mRNA and protein levels were significantly increased by 1 microM tt-DDE treatment. Co-treatment with vitamin C or NAC partially prevented tt-DDE-induced cell proliferation. In addition, the downstream targets of p27, including CDK4, cyclin D1 and phosphorylated-Rb proteins, increased in 1 microM tt-DDE-treated cells and these changes were prevented by NAC co-treatment. Therefore, these results suggest that tt-DDE increased cell proliferation via inhibition of p27 expression, increase in CDK4/cyclin D1 protein accumulation and enhancement of Rb phosphorylation. Increased cell proliferation is considered as the early stages of lung carcinogenesis. Administration of antioxidants may prevent COF-associated lung carcinogenesis.