The lipid-lowering effects of rosuvastatin and atorvastatin were determined across their dose ranges in a 6-week, randomized, double-blind trial. Three hundred seventy-four hypercholesterolemic patients with fasting low-density lipoprotein (LDL) cholesterol > or =160 but <250 mg/dl (> or =4.14 but <6.47 mmol/L) and fasting triglycerides <400 mg/dl (<4.52 mmol/L) and without active arterial disease within 3 months of entry received once-daily rosuvastatin (5, 10, 20, 40, or 80 mg [n = 209]) or atorvastatin (10, 20, 40, or 80 mg [n = 165]). The percentage decrease in plasma LDL cholesterol versus dose was log-linear for each drug, ranging from -46.6% to -61.9% for rosuvastatin 10 and 80 mg, compared with -38.2% to -53.5% for atorvastatin 10 and 80 mg. The dose curve for rosuvastatin yielded an 8.4% greater decrease in LDL cholesterol compared with atorvastatin at any given dose (p <0.001). Similarly greater decreases were observed for rosuvastatin across the dose range in total cholesterol (-4.9%), non-high-density lipoprotein (non-HDL) cholesterol (-7.0%), apolipoprotein B (-6.3%), and related ratios versus atorvastatin (all p <0.001). Because dose responses for HDL cholesterol, triglycerides, and apolipoprotein A-I were non-log-linear and nonparallel between the 2 drugs, percentage changes from baseline were compared at each dose. Significantly greater increases for rosuvastatin compared with atorvastatin were observed for HDL cholesterol at 40 and 80 mg, and for apolipoprotein A-I at 80 mg. Significantly greater triglyceride decreases were seen at 80 mg with atorvastatin over rosuvastatin. Both rosuvastatin and atorvastatin were well tolerated over 6 weeks.