Twenty-four men and 24 women, all nonsmoking, and maintaining normal dietary habits were assigned to 3 groups of 16. Each group comprising 4 males with "low" cholesterol levels (<6 mmol/L) matched for age and build with 4 males with "high" cholesterol levels (>6 mmol/L) and 8 similarly matched females. A three-treatment, three-treatment period, cross-over design was adopted. The three treatments were placebo, 60 mg vitamin C/day (the recommended daily allowance) and 6 g vitamin C/day for 14 days with 6 weeks between treatments. Blood samples were taken at the end of each treatment period. Vitamin C supplementation significantly increased plasma vitamin C concentrations and total antioxidant capacity, but did not affect cholesterol status or plasma ras p21 protein levels. There was a nonsignificant dose-related decrease in plasma lipid peroxidation breakdown products. DNA damage, measured in lymphocytes by the Comet assay and chromosome aberration test, was not increased after vitamin C supplementation. Sensitivity to hydrogen peroxide (in the Comet assay) was also unaffected, but sensitivity to chromosome aberration induced by bleomycin was increased by supplementation. A significant gender difference was found in plasma vitamin C levels, antioxidant capacity, and number of chromosome aberrations. Results were independent of low and high cholesterol status.