INTRODUCTION: The association of elevated plasma triglyceride concentrations, decreased HDL-cholesterol, and dense LDL (dLDL) is referred to as the atherogenic lipoprotein phenotype. dLDL particularly plays a role in the metabolic syndrome and type 2 diabetes and may be one of the factors responsible for the increased risk for coronary artery disease in these patients. The effect of fenofibrate and atorvastatin on the LDL subfraction profile in patients with combined hyperlipidemia and a preponderance of dLDL was studied in a sequential design. METHODS: Six male patients with combined hyperlipidemia and dLDL received 160 mg/die supra-bioavailable fenofibrate. After a washout phase of 8 weeks all patients received 10 mg/die atorvastatin for another 8 weeks. At baseline, after fenofibrate, and after atorvastatin treatment LDL subfractions were analyzed by equilibrium density gradient ultracentrifugation. RESULTS: Treatment with atorvastatin and fenofibrate reduced serum cholesterol by 30 % and 21 % (p = 0.046) (p-values for differences between treatment groups), triglycerides by 32 % and 45 %, LDL cholesterol by 28 % and 16 %, and increased HDL cholesterol by 3 % and 6 %, respectively. Atorvastatin and fenofibrate treatment resulted in the following changes of apoB and LDL subfractions: LDL-1 (1.019 – 1.031 kg/L) – 31 % and + 15 % (p = 0.028); LDL-2 (1.031 – 1.034 kg/L) – 14 % and + 57 % (p = 0.028); LDL-3 (1.034 – 1.037 kg/L) – 20 % and + 30 % (p = 0.028); LDL-4 (1.037 – 1.040 kg/L) – 25 % and – 6 %; LDL-5 (1.040 – 1.044 kg/L) – 29 % and – 38 %; and LDL-6 (1.044 – 1.063 kg/L) – 39 % and – 55 % (p = 0.028). As a consequence, fenofibrate reduced LDL density significantly (p = 0.028 versus atorvastatin). CONCLUSIONS: Atorvastatin decreased all LDL-subfractions to a similar extent (quantitative effect) whereas fenofibrate reduced predominantly dLDL and changed the LDL profile towards medium dense LDL-particles (qualitative effect). Since medium dense LDL have a higher affinity to the LDL-receptor fenofibrate may have a higher antiatherogenic potential than assessed by the reduction of total LDL-cholesterol and triglycerides alone.