Adipose tissue was obtained at thoracotomy in five control patients with valvular heart disease, all of whom were free of coronary artery disease and all of whom were normolipidemic with normal low density lipoprotein apolipoprotein B levels, and eight patients with coronary artery disease, all of whom had hyperapobetalipoproteinemia. In both groups, the rates at which linoleic acid and palmitic acid were incorporated into diglyceride and triglyceride were determined in vitro. The data indicate that fatty acid incorporation into adipose tissue glycerides was twice as rapid in controls as in patients with hyperapobetalipoproteinemia. By contrast there was no difference between the groups in the rate of net lipolysis of adipocyte glyceride. The data at hand do not establish the mechanism responsible for the difference in synthesis between normal subjects and patients with hyperapobetalipoproteinemia, but this may explain the delayed chylomicron triglyceride clearance previously observed in the disorder.