Epidemiological studies have strongly implicated active and passive smoking with increased risk of cardiovascular diseases. The present study was performed to determine if exposure to sidestream cigarette smoke (SSCS), a surrogate of environmental tobacco smoke, promotes atherogenesis in a mouse model of human atherosclerosis. Female ApoE-deficient mice, maintained on a Western diet, were exposed to SSCS in a whole-body exposure chamber for a total of 6 h each day, 5 days a week for 7, 10 and 14 weeks. Animals exposed to filtered ambient air served as controls. Elevated concentrations of blood carboxyhemoglobin and pulmonary CYP1A1 ascertained effective exposure of animals to SSCS. There were no consistent changes in serum concentrations of cholesterol between control and SSCS-exposed mice. Morphometric assessment of grossly discernible lesions covering the intimal area of aorta showed remarkable increases in SSCS-exposed mice at all three exposure durations studied. Increases in the lesion area defined by en face measurements were accompanied by parallel increases in the levels of esterified and unesterified cholesterol in the aortic tissues of SSCS mice. These results clearly demonstrate promotion of atherosclerotic lesion development by tobacco smoke in an atherosclerosis-susceptible mouse model.