Abstract Patterns of triacylglycerol (TG) turnover in plasma and liver, and the hepatic secretion of very low density lipoprotein triacylglycerol (VLDL TG) into the circulation, have been studied in young Large White female pigs, using i.v. tracer [1,3- 14C]- and [2- 3]glycerol. Serial measurements were made of plasma [ 14C]glycerol and [ 14C]glucose and of liver TG and plasma VLDL TG specific activities. In other studies VLDL TG obtained from a donor pig was reinjected into recipient animals to measure the early disappearance (dilution) of VLDL TG. Multicompartmental analysis revealed a mean rate of hepatic TG turnover somewhat slower than the rate of VLDL TG turnover, suggesting that almost all of the hepatic TG turnover was due to secretion of VLDL TG, and that the intestine probably contributed an appreciable part of the newly synthesized plasma VLDL TG. The t 1 2 of reinjected VLDL TG, whether prepared by the most rapid possible techniques and reinjected immediately or stored for several days, was approximately 10 min. This was much faster than the t 1 2 of the falling limb of the plasma VLDL TG curve seen after injection of labelled glycerol ( t 1 2 approximately 2 h). Thus, in these respects, the pig resembled all other species studied rather than human subjects as described by Farquhar et al.