Activities of antioxidant enzymes were measured in the erythrocytes from 15 smokers and 15 non-smokers. Superoxide dismutase (SOD) and catalase (CAT) activities were found lower but, glutathione peroxidase (GSH-Px) activity unchanged in the erythrocytes from smokers compared with non-smokers. Levels of thiobarbituric acid-reactive substances (TBARS) were however higher both in erythrocytes and plasma from smokers. Antioxidant vitamin (vitamins E and C) supplementation for the period of 15 days caused significant increases in the activities of all antioxidant enzymes and decreases in the TEARS levels of erythrocytes and of blood plasma in smoker group. It has been observed that smoking caused significant changes in the concentrations of plasma lipid fractions as well. In this regard, total cholesterol level (TC) was found unchanged, LDL cholesterol and triglyceride (TG) levels increased and HDL cholesterol decreased in the plasma from smokers compared with non-smokers. Vitamin supplementation caused a significant increase in HDL cholesterol and a decrease in LDL cholesterol in plasma from smokers. The vitamins normalised the HDL/LDL ratio in smokers. Fatty acid composition of erythrocyte membranes from smokers also presented significant changes. In particular, oleic acid (18:1) was almost absent in the erythrocyte membranes of smokers. In contrast, the relative amount of stearic acid (18:0) was found to be significantly increased but, those of some fatty acids (12:0, 14:0, 14:1 and 16:0) decreased in the erythrocyte membranes of smokers. Results suggested that enzymatic antioxidant defence system of erythrocytes was depressed and the erythrocytes were exposed to oxidant stress due to smoking. Increased plasma TEARS levels indicated that not only erythrocytes but also some other tissues and cells might be exposed to the radical stress by cigarette smoke. Smoking also caused significant changes in the levels of plasma lipid parameters and antioxidant vitamins partly protected erythrocytes against such harmful effects of smoking by scavenging free radical species and by activating and/or inducing antioxidant enzymes. (C) 1997 Elsevier Science Inc.