In this study, we investigated serum pro-oxidantantioxidant balance in 210 healthy subjects divided into groups with low and high atherogenic risk according to the levels of serum total cholesterol (TC) and low-density lipoprotein-cholesterol (LDL-C) and high-density lipoprotein- cholesterol (HDL-C). Diene conjugate (DC), malondialdehyde (MDA), polyunsaturated fatty acid (PUFA), vitamin E, and vitamin C levels and antioxidant activity (AOA) were determined in the serum. Endogenous DC and copperinduced MDA levels were also measured in the LDL fraction isolated by precipitation with buffered heparin from plasma in 80 healthy subjects with different serum LDL-C levels. Subjects with a high atherogenic risk had significantly higher plasma DC, MDA, and PUFA levels, but lower vitamin E/TC values and AOA than subjects with low atherogenic risk. Endogenous DC and copper-induced MDA levels in the LDL fraction were increased in subjects with serum LDL-C levels higher than 4.14 mM compared with those with normal LDL-C levels. In conclusion, this study clearly indicates that a disturbance in serum pro-oxidant-antioxidant balance and an increase in LDL oxidation are concomitant with higher TC and LDL-C and lower HDL-C levels in the serum.