This study was conducted to determine whether chylomicron remnants accumulate in the plasma of patients with "endogenous" hypertriglyceridemia. Retinyl esters were used as markers of chylomicrons and chylomicron remnants since they are carried mainly if not exclusively by lipoproteins of intestinal origin. Seventy-six fasting normotriglyceridemic and hypertriglyceridemic patients were studied 12 to 15 hours after ingesting 25,000 IU of vitamin A. Plasma retinol and retinyl esters were measured by reversed-phase high-performance liquid chromatography. Chylomicronemia was assessed by flotation at unit gravity and by chylomicron flocculation in 3% polyvinylpyrrolidone. Plasma lipids, retinoids, lipoprotein cholesterol, and the electrophoretic mobility of very-low density lipoproteins were determined in a subset of 36 subjects. Progressively elevated plasma retinyl ester concentrations were observed among patients with mild, moderate, and severe hypertriglyceridemia. All subjects with fasting chylomicronemia had retinyl ester retention. The majority of subjects with mild or moderate hypertriglyceridemia (predominantly type IV hyperlipoproteinemia) also had elevated plasma concentrations of retinyl esters. Total plasma retinyl ester and plasma triglyceride concentrations correlated significantly (rs = 0.721, P less than 0.001) in nonchylomicronemic subjects. In addition, total plasma retinol concentrations were mildly elevated among hypertriglyceridemic subjects because retinol, as well as retinyl esters, is transported by triglyceride-rich lipoproteins. If lipoprotein remnants are atherogenic in man, then chylomicron remnant retention may accelerate atherogenesis in hypertriglyceridemic individuals.