Combined hyperlipidemia (CHL) is characterized by a concomitant elevation of plasma levels of triglyceride-rich, very low density lipoproteins (VLDLs) and cholesterol-rich, low density lipoproteins (LDLs). The predominance of small, dense LDLs contributes significantly to the premature development of coronary artery disease in patients with this atherogenic dyslipoproteinemia. In the present study, we evaluated the impact of atorvastatin, a newly developed inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase, on the cholesteryl ester transfer protein (CETP)-mediated remodeling of apolipoprotein (apo) B-containing lipoprotein subspecies, and more specifically, the particle subpopulations of VLDL and LDL in CHL. In parallel, we evaluated the atorvastatin-induced modulation of the quantitative and qualitative features of atherogenic apo B-containing and cardioprotective apo AI-containing lipoprotein subspecies. Atorvastatin therapy (10 mg/d for a 6-week period) in patients with a lipid phenotype typical of CHL (n=18) induced reductions of 31% (P<0.0001) and 36% (P<0.0001) in plasma total cholesterol and LDL cholesterol, respectively. In addition, atorvastatin significantly reduced VLDL cholesterol, triglycerides, and apo B levels by 43% (P<0.0001), 27% (P=0.0006), and 31% (P<0.0001), respectively. The plasma concentrations of triglyceride-rich lipoproteins (VLDL1, Sf 60 to 400; VLDL2, Sf 20 to 60; and intermediate density lipoproteins, Sf 12 to 20) and of LDL, as determined by chemical analysis, were markedly diminished after drug therapy (-30% and -28%, respectively; P<0.0007). Atorvastatin significantly reduced circulating levels of all major LDL subspecies, ie, light (-28%, P<0.0008), intermediate (-27%, P<0.0008), and dense (-32%, P<0.0008) LDL; moreover, in terms of absolute lipoprotein mass, the reduction in dense LDL levels (mean -62 mg/dL) was preponderant. In addition, the reduction in plasma dense LDL concentration after therapy was significantly correlated with a reduction in plasma VLDL1 levels (r=0.429, P=0.0218). Atorvastatin induced a significant reduction (-7%, P=0.0039) in total CETP-dependent CET activity, which accurately reflects a reduction in plasma CETP mass concentration. Total CETP-mediated CET from high density lipoproteins to apo B-containing lipoproteins was significantly reduced (-26%, P<0.0001) with drug therapy. Furthermore, CETP activity was significantly correlated with the atorvastatin-induced reduction in plasma VLDL1 levels (r=0.456, P=0. 0138). Indeed, atorvastatin significantly and preferentially decreased CET from HDL to the VLDL1 subfraction (-37%, P=0.0064), thereby reducing both the levels (-37%, P=0.0001) and the CE content (-20%, P<0.005) of VLDL1. We interpret our data to indicate that 2 independent but complementary mechanisms may be operative in the atorvastatin-induced reduction of atherogenic LDL levels in CHL: first, a significant degree of normalization of both the circulating levels and the quality of their key precursors, ie, VLDL1, and second, enhanced catabolism of the major LDL particle subclasses (ie, light, intermediate, and dense LDL) due to upregulation of hepatic LDL receptors.