Intimal accumulation of macrophages and changes in the phenotype and growth properties of vascular smooth muscle cells (SMCs) represent key events in the development of atherosclerotic lesions. Here we report on the in vivo effect exerted by nitrendipine on aortic tissue of cholesterol-fed rabbits. We have focused especially on the myosin heavy chain (MyHC) pattern expressed by aortic SMC, taken as a marker of cell differentiation. Using monoclonal antibodies specific to the different forms of MyHC, three differentiation steps were determined: adult, postnatal, and fetal. Nitrendipine administered in conjunction with a cholesterol-enriched diet reduced the development of atherosclerotic lesions (atherosclerosis index: 0.21 vs. 0.32 in untreated animals, p < 0.005), despite persistently high serum cholesterol levels. Compared to untreated controls, nitrendipine-treated animals displayed a decreased number of postnatal-type SMCs in the media underlying the plaque (prevalence index: 0.07 vs. 0.26, p < 0.0001 and a lower aortic cholesterol content (free cholesterol: 3.3 vs. 11.5 ng/mgp < 0.0001; esterified cholesterol: 7.2 vs. 40.5 ng/mg, p < 0.0001). Moreover, nitrendipine treatment decreased the intimal accumulation of macrophages and fetal-type SMCs. It is conceivable that calcium antagonists may exert their antiatherogenic effect, at least in part, through cellular changes unrelated to the classical risk factors.