The expression of inducible nitric oxide synthase (iNOS) as well as its functional activity has recently been reported in atherosclerotic lesions. The aim of the present study was to evaluate the expression of iNOS in various arteries of rabbits fed a long-term but low-level cholesterol-enriched diet which promotes different types of atherosclerotic lesions resembling human diseased vessels. No iNOS expression was revealed in arteries from control rabbits and in fatty streaks found in carotid and femoral arteries from hypercholesterolemic rabbits. In transitional lesions from the thoracic and abdominal aortas, the coronary and pulmonary arteries, a punctiform iNOS staining was detected in the intima. When lesions were more advanced, iNOS expression was found more intense and diffuse and localized in the subendothelial layer as well as in the media. Smooth muscle cell accumulation in intimal layers of the arteries is a marker of the degree of evolution of the atherosclerotic lesion; since we found a correlation between the smooth muscle cell infiltration in the intima and the iNOS expression in the intima and the subendothelial layer, our results suggest a link between the severity of the lesion and the iNOS expression.