Postprandial lipoprotein metabolism may play a role in the etiology of premature coronary artery disease (CAD). To determine whether apolipoprotein E (apo E) polymorphism and the size of low density lipoprotein (LDL) influence postprandial lipemia we studied 39 healthy men and 35 men with CAD. Venous blood samples were obtained before an oral fat load and 3, 5 and 7 h thereafter. Total cholesterol and high density lipoprotein (HDL) cholesterol concentrations did not change in either group during the fat load, but triglycerides increased more markedly in CAD patients compared with controls independently of apo E phenotypes. There was a positive correlation between the size of LDL and the concentration of HDL cholesterol (r = 0.541, P < 0.001); conversely, an inverse correlation was observed between LDL size and the level of fasting triglycerides (r = -0.582; P < 0.001). The patients with CAD had significantly smaller LDL particles (25.89 +/- 0.56 nm) than in controls (26.21 +/- 0.63 nm) (P < 0.05). The increase in triglyceride levels during the fat load was highest in CAD patients with a small size of LDL particles (< 25.5 nm) and lowest in controls with large LDL (> 25.5 nm). Our results suggest that the magnitude of the triglyceride response is a better indicator of CAD risk than the fasting triglyceride concentration. The best model in our logistic regression analysis selected as significant risk factors the change of triglyceride concentration from the baseline at 5 h after a fat meal and HDL cholesterol. This model classified 83% of the subjects correctly.