O ur primary aim was to determine the extent to which intraplasmic retinyl palmitate (RP) transfers to other lipoprotein particles when chylomicron remnants are not produced and/or the plasma RP residence time is increased. The study was conducted on three familial type I hyperlipoproteinemic patients, four lipoprotein lipase (LpL)-deficient heterozygotes, and three controls on a metabolic research unit. To each subject, a fat load was administered containing 16% of total daily calories in type I patients, 40% in heterozygotes and controls, plus 60,000 U/m2 vitamin A. Triglyceride (TG) and RP levels were evaluated in chylomicron and nonchylomicron fractions. Delay in the clearance of chylomicron fraction RP and the marked deficiency in nonchylomicron-RP (presumed lack of remnant production) in all three type I patients suggests that RP does not demonstrate significant intraplasmic transfer from chylomicrons to existent apolipoprotein B100 particles. In contrast to noncoincident TG and RP peaking in the normal subject, heterozygotes were found to demonstrate coincident plasma TG and RP curves, which is consistent with a common catabolic pathway for both TG and RP and inconsistent with intraplasmic RP transfer. This corroborates reports on compromised chylomicron clearance in heterozygotes. We conclude that RP is an appropriate representative marker for intestinally derived particles in LpL-deficient or partially deficient individuals.