The efficiency of clearance of plasma triacylglycerols (TAG) after fatty meals in non-diabetic Caucasian subjects is believed to determine the plasma level of high-density-lipoproteins-cholesterol (HDL-C). It is unknown if this observation holds in diabetic subjects and in other racial groups. In assessing the factors that determine TAG responses to acute fat loading in a tropical African population with a low prevalence of atherosclerotic disease, twenty (nine obese) non-insulin-dependent diabetic (NIDDM) patients with optimal glycaemic control and twelve (six obese) age-matched non-diabetic subjects were given meals containing 50 g fat (in butter) and 75 g carbohydrate (in white bread) over 15 min in the morning after a 12 h overnight fast. The fasting plasma levels of glucose, TAG, total cholesterol (total-C), HDL-C, low-density-lipoprotein-cholesterol, insulin and glycosylated haemoglobin (HBAlc) were estimated; glucose and TAG levels were also measured postprandially for 8 h at 2 h intervals. Postprandial lipaemia was consistently higher in the diabetic patients (about 50–100% more than values obtained in the non-diabetic subjects, even when corrected for differences in body mass) and correlated positively with age and postprandial glycaemia. This defect in TAG clearance was even worse (by about 50%) when glucose tolerance became further impaired after ten of the diabetic patients stopped oral hypoglycaemic treatment for 1 week and the fat-tolerance test was repeated. In the obese non-diabetic subjects, but not those of normal weight, there were significant negative relationships between the postprandial lipaemia and fasting plasma levels of HDL-C and the HDL-C: total-C ratio, as reported in Caucasians. It is concluded that age and the ambient glucose concentration appear to be the important determinants of the efficiency of TAG clearance in diabetic subjects. This accords with clinical observations of increased atherogenic liability with increasing age and poorer glycaemic control. The determinants in non-diabetic subjects were less defined, indicating that postprandial lipaemia might be influenced by various factors (obesity as shown here) in different subsets of individuals.