Mapping the distribution of an immature smooth muscle cell (SMC) subpopulation in large- and small-sized arterial vessels was carried out in normocholesterolemic rabbits and compared with the mapping atherosclerotic lesions in endogenously (Watanabe heritable hyperlipemic, WHHL) and exogenously derived (cholesterol-fed, CT) hypercholesterolemic rabbits. This cell subset is identified by a specific myosin isoform content and displays an intermediate degree of differentiation between fetal- and adult-type SMC. Monoclonal anti-myosin antibodies, immunofluorescence procedures, and different arterial segments of a rabbit vessel tree, i.e. from aorta to dental pulp (common carotid, external carotid, lingual, facial, maxillary, inferior alveolar arteries, and dental branches of alveolar arteries) were studied. WHHL of different ages (3 to 12 months), and two different concentrations of CT (2% and 0.2%) in the diet for 3 and 12 months, respectively, were used. The results of the present study indicate that: (1) using a diet with a higher percentage of CT (rabbits fed 2% CT-diet for 3 months) there is maximum expansion of atherosclerotic lesions from the aorta up to the maxillary artery; (2) localization of atherosclerotic lesions with a lower CT content in the diet is dependent on the duration of feeding and may involve the aorta up to the external carotid artery; (3) the development of the atherosclerotic lesion in hypercholesterolemic rabbit is strictly related to the appearance of an intermediate SMC subtype; (4) atherosclerotic lesions occur only in those arterial sites which, in corresponding normocholesterolemic rabbit, contain intermediate-type SMC; and (5) no differences can be found in the distribution of SMC subpopulations present in the lesions from WHHL, CT-fed animals, or at various arterial levels, whereas some discrepancies can be shown in aortic atherogenesis.