Cigarette smoke extract dose-dependently caused lipid peroxidation measured as 4-hydroxy-2-nonenal levels in alveolar epithelial cells as well as in primary human small airway epithelial cells. A. Transformed alveolar epithelial cells were exposed to cigarette smoke (1R3F) extract (1.0 – 5.0 %) for 24 hr and the extent of lipid peroxidation was determined by measuring 4-HNE levels. Cigarette smoke extract increased the levels of 4-HNE in all the five transformed alveolar epithelial cell lines in dose-dependent manner. However, the baseline levels of 4-HNE were varied amongst the cell lines, H1299 with lower base line levels and MLE-15 with higher baseline levels. B. Primary human small airway epithelial cells (SAEC) were exposed to cigarette smoke extract (0.2%-1.0 %) derived from 1R3F research grade cigarettes for 24 hr, and the levels of 4-HNE were measured. Cigarette smoke extract dose-dependently increased the levels of 4-HNE levels SAEC. Data represent mean ± SEM of 3 individual experiments. §p < 0.001 compared to control values. CSE: cigarette smoke extract.