Polymorphism of the fatty acid-binding protein 2 (FABP2) gene has been shown to affect the affinity of intestinal FABP for fatty acids. This could cause changes in postprandial triglyceride metabolism. In the present study, postprandial lipemia was studied in normotriglyceridemic subjects with genetic variation in the FABP2 gene. Oral fat-loading tests were performed in 8 subjects homozygous for the Thr-encoding allele at codon 54 of the FABP2 gene and in 7 subjects homozygous for the Ala-encoding allele (wild type). There were no significant differences between these 2 groups in age, body mass index, fasting plasma triglyceride and cholesterol levels, or fasting glucose and insulin levels. The increase of plasma triglyceride concentration after the fat test meal was significantly greater in subjects who were homozygous for the Thr-54 allele (area under the response curve, 4.27+/-1.31 versus 2.49+/-1.18 mmol/L x h-1, P=0.04). The difference was seen in both chylomicron (2.51+/-0. 98 versus 1.41+/-0.74 mmol/L x h-1, P=0.03) and very low-density lipoprotein triglycerides (1.57+/-0.77 versus 0.99+/-0.40 mmol/L x h-1, P=0.04). Postprandial triglyceride response correlated with fasting triglycerides in the Ala-54 homozygotes (r=0.79, P=0.05) but not in the Thr-54 homozygotes (r=0.09), who showed a strong correlation between triglyceride and insulin responses (r=0.83, P=0. 02). With reservations related to a small number of subjects studied, these results indicate that the Thr-encoding allele of the FABP2 gene is associated with increased postprandial lipemia. The lipemic response was associated with postprandial insulin response, suggesting that in the Thr-54 homozygotes, altered postprandial lipemia may also modify insulin action or vice versa.