This study was performed to gain information about the influence of two cardiovascular risk factors, cigarette mainstream smoke (MS) and high-cholesterol/fat diet, on the progression of atherosclerosis in apolipoprotein E-deficient (Apo E-/-) mice. Eight to 12-week-old mice were whole-body exposed for up to 12 months (6 h/day, 5 days/week) to diluted cigarette mainstream smoke at total particulate matter (TPM) concentrations of 100 or 200mg/m(3), or to filtered fresh air (sham) in combination with a normal chow diet or a high-cholesterol/fat diet. Cholesterol in the aortic arch was elevated in the high-cholesterol/fat diet groups exposed to 200 mg TPM/m(3) compared to sham at all time points. In the brachiocephalic artery (BA), absolute plaque size and fraction area of plaques was elevated over the 12-month time course in mice exposed to 200 mg TPM/m(3) compared to sham (both diets). Exposure to 100 and 200 mg TPM/m(3) altered the number of elastin-rich layers in the BA in mice fed a high-cholesterol/fat diet, indicating changes in plaque morphology at 6 and 9 months. This study shows for the first time the influence of two different risk factors, MS and high-cholesterol/fat diet, both alone and in combination over a period of 12 months, on the progression of atherosclerosis in Apo E-/- mice. Data suggest that long-term exposure to cigarette mainstream smoke accelerates the development of atherosclerosis in Apo E-/- mice, particularly in combination with a high-cholesterol/fat diet.