Beneficial effects of dietary supplementation with antioxidant vitamins are attributed mainly to the influence upon lipid metabolism, endothelial and vascular functions. Their effect upon leucocyte oxygen free radical producing capacity has not been investigated. In 13 healthy volunteers we examined the influence of oral supplementation with vitamins C and E (aa 600 mg per day for 14 days) upon leucocyte oxygen free radical production estimated by lucigenin-amplified chemiluminescence in isolated leucocytes stimulated with arachidonic acid. After supplementation with vitamins, significant increase in serum content of ascorbic acid and tocopherol was concomitant with significant (P < 0.001) decrease of leucocyte chemiluminescent response (mean 63.2 + 23.0 SD, % of initial values) and lowering of serum lipid peroxides (P < 0.05). These findings suggest that suppression of leucocyte capacity to produce oxygen free radicals as shown in this study, may contribute to vasoprotective action of vitamins C and E.