A low HDL cholesterol level is frequently but not consistently associated with inefficient postprandial fat clearance. We studied triglycerides, retinyl palmitate and squalene and apolipoprotein B-48 after a fat loading test in one subject heterozygous for a novel point mutation of apolipoprotein A-I (A-IFIN, Leu 159-->Arg) and low HDL cholesterol level without coronary artery disease, and in 16 healthy controls with the same apolipoprotein E phenotype, 3/3, as the proband. HDL cholesterol and apolipoprotein A-I levels were 0.32 mmol/l and 57 mg/dl in the proband, and 1.29 +/- 0.12 mmol/l (mean +/- S.E.) and 126 +/- 4 mg/dl in the controls. The peak concentration for triglycerides in plasma, chylomicrons and VLDL occurred at 4 h both in the case and controls. However, the peak concentrations for retinyl palmitate and squalene in chylomicrons and VLDL were delayed to 12 h in the proband compared with 4 and 9 h in the controls. The peak of apolipoprotein B-48 occurred at 6 h in the proband and at 4 h in the controls, so that triglycerides, apolipoprotein B-48 and retinyl palmitate and squalene peaked differently. After 24 h, retinyl palmitate, squalene, and apolipoprotein B-48 had returned to the baseline levels. The results show for the first time an impaired postprandial lipoprotein removal in a case heterozygote with moderately low HDL cholesterol due to an apolipoprotein A-1 mutation not associated with coronary artery disease.