Smooth muscle cells (SMC) were cultured from atherosclerotic plaques and uninvolved arteries to determine if differences exist between growth characteristics or ultrastructure of the cultured cells. Eighteen aortic punch biopsies provided the uninvolved tissue, and 58 carotid plaques provided the atherosclerotic tissue. Eighty percent of the sample yielded viable cultured cells, which reached a maximum population doubling time during log phase growth of 72 h (seeding density=1.0×104 cells/cm2, 2nd passage). Growth characteristics of both normal and plaque-derived cells were the same in vitro. Growth rate declined with time in culture, and cell division ceased by the 5th or 6th passage. In culture, spindle shaped cells formed the “hill and valley” configuration typical of SMC. Plaquederived SMC were ultrastructurally similar to SMC from uninvolved vessel wall. Proliferative potential did not vary with age of sex, with method of culture, or with whether the cells were plaque derived or not.