This study was designed to examine changes of hemorheological parameters in patients with CHD and hypercholesterolaemia (wide range of plasma total cholesterol level from 5.6 to 9.8 mmol.l-1) subjected to lipid lowering therapy with statins (simvastatin, 10.0-20.0 mg/day, dosage was dependent on an initial level of total cholesterol). Twenty female subjects were enrolled in this research program. Both prior to and following drug treatment for eight weeks, hemorheological measurements included plasma viscosity, high and low shear whole blood viscosity, hematocrit, RBC aggregation and rigidity. Treatment with simvastatin significantly (p<0.05) reduced total cholesterol, total triglycerides and low-density lipoprotein cholesterol (LDL-C). However, the hemorheological effects of lipid lowering therapy differed markedly between macro- and microrheological groups of parameters: plasma and whole blood viscosity were not significantly changed whereas RBC aggregation and its rigidity were decreased significantly after statin treatment. These results thus suggest that the rheologic effect of lipid lowering therapy concerned mainly the microrheological parameters: red cell aggregation and deformability.