It has been reported that smokers have higher plasma malondialdehyde concentrations compared with non-smokers. However, smokers have also consistently been shown to have a lower intake of fruits and vegetables as well as lower plasma antioxidant concentrations. Since both the latter issues may well influence the malondialdehyde concentration, we wanted to investigate if the observed difference between smokers and non-smokers was a result of differences in antioxidant status or if a more direct effect of smoking could also be isolated. In the present study, the plasma malondialdehyde and antioxidant profiles of a cohort of smokers (n 48) and non-smokers (n 32) were compared. While there was no significant difference in the major plasma antioxidants measured, i.e. ascorbic acid, α- and γ-tocopherol and uric acid, we found a significant effect of smoking on plasma malondialdehyde (P=0·0003). Consequently, the present study suggests that lipid peroxidation as measured by plasma malondialdehyde is induced by smoking per se. While poor antioxidant status presumably also affects lipid peroxidation, it is only partly responsible for the increased level found in smokers in general.