The effects and tolerability of the new HMG-CoA reductase inhibitor rosuvastatin were assessed in 68 hypercholesterolemic Japanese patients (22 men and 46 postmenopausal women; age range 28-72 years) in a multicenter, double-blind, dose-ranging, early phase II study. Patients were randomized into three groups and received once-daily doses of 1, 2, or 4 mg rosuvastatin. Sixty evaluable patients (19 men and 41 women) with mean total cholesterol (TC) 294 mg/dl (7.60 mmol/l) and mean triglyceride (TG) 150 mg/dl (1.69 mmol/l) provided data in the efficacy analysis based on percentage changes in lipids at 4 and 8 weeks. All doses of rosuvastatin improved lipid parameters after both 4 and 8 weeks of therapy. On average, TC decreases were 22-29%, low-density lipoprotein cholesterol (LDL-C) decreases 32-42%, TG decreases 2% to 22%, and HDL-C increases 3-7%. There were no remarkable differences between efficacy at 4 and at 8 weeks, and dose-dependent reductions were noted for LDL-C, with 30, 39, and 42% decreases in the 1-, 2-, and 4-mg/ day dose groups, respectively, at 8 weeks. The drug was well tolerated over the 8 weeks of therapy. These preliminary results indicate that rosuvastatin is a potent cholesterol-lowering agent, capable of achieving marked reductions in LDL-C even at low doses.