Human arterial biopsies were studied by morphometrical, cytochemical, autoradiographic and ultrastructural methods with the aim of determining whether intimal lesions in atherosclerosis are characterized by definite cytological patterns. The results have shown: 1. a strong association between fibro-atheromatous plaques and foam and monocyte-like cells; 2. very few foam cells in diffuse intimal thickening and pearly-white fibrous plaques; 3. macrophages and foam cells were the only cytotypes consistently labelled with 3H-TdR and presumably proliferating in the fibro-atheromatous plaques.