It is unknown whether the clearance of atherogenic chylomicron remnants and the postprandial lipoprotein metabolism in general can be improved by 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors in subjects with familial combined hyperlipidemia (FCH). Therefore, the postprandial chylomicron remnant clearance was studied in nine normolipidemic untreated controls and seven FCH patients before and after treatment with simvastatin using an oral vitamin A-fat load (24 hours, 50 g/m2). Treatment with simvastatin reduced plasma cholesterol level by 16% (mean +/- SEM, 8.1 +/- 0.8 v 6.8 +/- 0.8 mmol/L; P < .05) and plasma apolipoprotein (apo) B level by 19% (1.6 +/- 0.2 v 1.3 +/- 0.2 g/L; P < .05). Plasma apo E level (89.6 +/- 21.0 mg/L) was reduced by 29% (63.5 +/- 14.1 mg/L; P < .05). High-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) levels did not change; consequently, the reductions seen had been due to a decrease in very-low-density lipoprotein (VLDL) levels. Fasting plasma triglyceride (30% reduction) and plasma apo C-II (31% reduction) levels did not change significantly. Mean postheparin plasma lipoprotein lipase (LPL) activity increased by 13% after treatment (90.4 +/- 19.8 v 102.6 +/- 20.3 mU/mL; P < .05), but hepatic lipase (HL) activity was not altered. The clearance of chylomicrons (Sf > 1,000), expressed as the area under the 24-hour retinyl palmitate curve, did not change with simvastatin (52.8 +/- 12.9 v 51.8 +/- 13.4 h.mg-1/L).(ABSTRACT TRUNCATED AT 250 WORDS)