Smooth muscle cells isolated from atherosclerotic lesions of human aorta retain in primary culture their intrinsic in vivo characteristics: namely, enhanced proliferative activity and high lipid levels. We have tested the effect of different compounds on [3H]thymidine uptake and on the levels of phospholipids, triglycerides, cholesterol, and cholesteryl esters in cultured aortic cells. Effects, such as the inhibition of cellular proliferation and/or lowering of the intracellular lipid levels which would be regarded as antiatherosclerotic if exerted in vivo, were observed in vitro by the following compounds: dibutyryl cyclic AMP, cholera toxin, forskolin, methylisobutylxanthine, stable prostacyclin analogues, prostaglandins E2 and D2, verapamil, reserpine, alpha-tocopherol, butylated hydroxytoluene, lipostabil, and high density lipoproteins. In this paper, we discuss the possibility of using a primary culture of smooth muscle cells from an atherosclerotic human aorta for testing drugs for possible antiatherosclerotic activity.