High resolution B-mode ultrasonography of the carotid arteries has been used to investigate the signs of early atherosclerotic vessel wall disease by measuring the intima-media thickness (IMT). We examined the association between IMT and lipid peroxidation and found IMT to be increased in a group of patients with respect to controls (1.430 +/- 0.341 mm versus 0.703 +/- 0.201 mm, P < 0.001). Plasma and erythrocyte malondialdehyde (MDA) levels were also significantly higher (P < 0.001) and the erythrocyte reduced glutathione (GSH) levels were significantly lower (P < 0.001) in the patients with respect to the controls. In the groups of patients there was no significant correlation between the mean IMT and the plasma and erythrocyte MDA levels or the erythrocyte GSH levels. In conclusion determination of lipid peroxides would be especially important and advisable in patients with increased carotid IMT. Type II diabetes and hypertension were also associated with increased IMT. (C) 1998 Elsevier Science B.V. All rights reserved.