Rats fed on atherogenic diets containing 2% cholesterol and 0.5% cholic acid with or without 0.15% thiouracil were exposed to carbon disulphide (CS2) vapours (1 mg/l of air), five hours a day, six days a week for 6-10 months. Serum and aorta lipid contents were determined, and the extent of atherosclerotic changes was investigated. The following effects of chronic exposure to CS2 were found: (1) slower gain in body weight when rats were fed on atherogenic diet; (2) greater increase in serum cholesterol content (after thiouracil supplemented diet); (3) moderate increase in total cholesterol content in the aorta wall with a significantly increased esterified cholesterol fraction but none in phospholipid level in this tissue; and (4) more advanced lipid infiltrates of coronary arteries and endocardium, the latter predominantly in the aortic valves. These results together with data from previous studies indicate that metabolism of arterial lipids participates in the process of artheroma formation after chronic exposure to CS2 vapours.