The primary objective of these studies was to screen the materials showing inhibitions of HMG-CoA reductase in vitro. The secondary objective was to determine the effect of garlic, lovastatin and copper on cholesterol concentrations in plasma. liver and brease muscle of pullets. In experiment 1, the degree of inhibition of the selective samples on HMG-CoA reductase activity was determined in vitro. The inhibition rate of water soluble garlic extracts, lovastatin and copper to HMG-coA reductase activity were 51.3%, 87.5%, and 82.0% respectively . In experiment 2, control diet (basal diet), garlic powder (3% in diet) , lovastatin (300mg/kg of diet) and copper(200mg/kg of diet) were fed to pullets in order to investigate the changes of cholesterol concentration in plasma and tissues. Plasma total cholesterol , and LDL-cholesterol were significantly reduced in pullets fed a diet containing 3 % garlic powder. However, coper significantly increased total cholesterol compared to controls and lovastatin did not affect plasma chholesterol concentration . Total cholesterol inlover and breast muscle inpullets were not affectedb y adding cholesterol lowering materials to the diets. The data suggests that it is not easy for HMG-CoA reductase inhibitors to reduce cholesterol levels in the body due to complication in cholestrol metabolism . However, garlic administration can lower the levels of plasma cholesterol in pullets.