Five healthy male subjects and five patients with mild hypertriglyceridemia were studied following the administration of 800-kcal liquid meals containing 40% of energy from fat, 40% from carbohydrate, and 20% from protein. On the first day of the study, the fat source was corn oil (long-chain triglyceride), whereas medium-chain triglyceride (MCT) oil was used the second day. Meals were infused into the duodenum using a peristaltic pump. Plasma samples, obtained at hourly intervals for 8 hours, were analyzed for glucose, cholesterol, triglyceride, and apolipoproteins C-II and C-III. The distribution of apoC-II and apoC-III between ultracentrifugally-separated triglyceride-rich lipoproteins (TRL) and high-density lipoproteins (HDL) was also evaluated. The patient group had significantly elevated fasting levels of triglyceride, apoC-II and apoC-III, as well as much greater lipemic response to the meal containing corn oil. In both groups, TRL apoC-II and apoC-III levels were positively correlated with the triglyceride level as it increased following the corn oil meal. These correlations were also observed in the normal subjects when the MCT oil meal was administered, even though changes in plasma triglycerides were minimal. In normal subjects, whole plasma levels of apoC-II and apoC-III decreased significantly following the meal containing corn oil, whereas no net changes occurred following the MCT oil meal. In hypertriglyceridemic subjects, small decreases in plasma apoC-II and apoC-III levels occurred after both meals, although the changes in apoC-II were not statistically significant. The tendency for decreased plasma apoC levels following alimentary lipemia confirms previous reports, and provides further data to support the concept that some apoC is cleared from plasma in association with TRL remnants. The finding that mildly hypertriglyceridemic subjects responded similarly to both conventional fat and MCT may indicate that their rates of remnant clearance were similar following the two meals.