Abstract Glycosaminoglycan (GAG) and lipid synthesis in smooth muscle cells cultured from normal and atherosclerotic rabbit aortas were studied. The incorporation of [ 14C]glucosamine into acidic GAGS, taken to represent their synthesis rate, was enhanced in cells from atherosclerotic aortas as compared with controls. The synthesis of sulphated glycosaminoglycans was affected most and the percentage of radioactivity incorporated into sulphated GAGs was 48 ± 3% in cells from atherosclerotic and 38 ± 4% in cells from healthy aortas. Non-radioactive GAGS secreted into incubation media were fractionated by electrophoresis. There was an elevated ratio of sulphated GAGs to hyaluronic acid in the cultures of cells from atherosclerotic aortas and the fraction corresponding to dermatan sulphate was increased most. The incorporation of [ 3H]oleate into phospholipids was enhanced in cells from atherosclerotic aortas indicating more rapid synthesis of this lipid fraction in these cells. Concentrations of free and esterified cell cholesterol were similar. The results indicate that the enhanced synthesis of sulphated GAGS typical of proliferative atherosclerosis in vivo is maintained in the third passage cultures of cells from atherosclerotic rabbit aortas. In addition there was an enhancement in the synthesis of phospholipids in these cells.