AbstractWe have estimated the turnover and relative pool sizes of nascent‐VLDL‐TG and VLDL‐remnants‐TG in anesthetized rats. [1‐14C]Palmitoyl‐ and [2‐3H]glyceryl‐labeled “VLDL”‐TG (including nascent VLDL‐TG and VLDL‐remnants‐TG) were prepared by injecting labeled palmitate and glycerol into donor rats. Labeled serum from these rats was then injected intravenously into nembutalized male rats and serial blood samples taken for 30 min. Special care was taken to define any early components in the labeled “VLDL”‐TG disappearance curves. In other experiments, the donors were rendered functionally hepatectomized 30 min after injection of3H‐glycerol and the endogenous labeled VLDL‐TG was allowed to circulate 30–60 min before collection of the TG‐labeled VLDL‐remnants‐containing serum. The latter was injected into 4 recipient nembutalized rats and the remnant‐TG‐turnover measured by serial sampling as above. In two cases,14C‐“VLDL” and3H‐VLDL‐remnants were injected as a single bolus into ether‐anesthetized rats. Despite its complex composition, “VLDL”‐TG in most cases disappeared in a single exponential fashion for 30 min with an average half‐life of 5.9 min in nembutalized and 2.8 in ether‐anesthetized rats. VLDL‐remnants‐TG showed a more complex behavior, but contained a major rapid component with a mean t1/2 of ca. 1.5 min in both groups. The data, analyzed by multicompartmental analysis, were fitted to a simple model in which turnover of a larger nascent VLDL‐TG pool with formation of a more rapidly turning over smaller pool of VLDL‐remnant‐TG is the rate‐limiting step in overall TG removal from the d<1.006 fraction of rat serum. The data are consistent with our theoretical prediction that under these conditions the kinetics of the VLDL‐remnants cannot be resolved from analysis of the total composite “VLDL” (nascent plus remnant) pool.