tory chow significantly reduced serum triglyceride levels by 6 hr and concomitantly decreased the rate of glycerol4C incorporation into hepatic and serum glycerides, in vivo. These changes persisted for at least 14 days. A similar decrease in serum triglyceride and glycerol incorporation into hepatic glycerides was observed in rats fed high glucose diets containing 0.25% CPIB. Serum glycerol was reduced by feeding CPIB for 14 days. The formation of diglyceride and triglyceride from 14C-snglycerol-3-P by rat liver homogenates was inhibited by addition of 1-40 mm CPIB to the reaction mixture. These results suggest that CPIB reduces hepatic glycerolipid synthesis, possibly by inhibition of one or more reactions in the esterification of sn-glycerol-3-P. This change may account for the early fall in serum triglyceride. At later time periods, serum glycerol levels fall and in some experiments, hepatic triglyceride content increases. Therefore, it is likely that additional metabolic alterations may contribute to the sustained hypotriglyceridemic effects of CPIB.