The postprandial (PP) elevations in triglyceride rich lipoproteins (TRL) are potentially atherogenic. We compared PP lipemia in non insulin dependent diabetes mellitus (NIDDM) with hypoalphalipoproteinemia (HA) and patients with primary HA. Eight males in each group, mean age +/- SD 54 +/- 10 years, were studied for 12 hours after the ingestion of a fat load (65 g of fat/square meter of body surface). Plasma glucose, triglycerides (TG) and cholesterol (C) in plasma and in the different lipoprotein fractions were measured. The PP triglyceridemia was significantly greater in NIDDM patients with HA and correlated with the fasting TG concentrations. The curve pattern of the lipemia (% delta) was otherwise similar in the patients with secondary or primary HA; only the triglyceridemia persisted for a longer period of time in the latter but was otherwise similar to that of the NIDDM patients with lower basal triglyceride values. Patients with primary HA may have a disturbed metabolism of triglyceride rich lipoproteins which have a delayed depuration during the postprandium. Basal HDL-C in patients with HA cannot predict the PP triglyceridemia.