The comparison was undertaken between the effects of ascorbate versus ascorbate plus iron supplementation on DNA damage. Twenty healthy subjects with initial levels of plasma ascorbate of 67.2 +/- 23.3 mu mol/l were randomly assigned to and cycled through one of three supplementation regimes: placebo, 260 mg/d ascorbate, 260 mg/d ascorbate plus 14 mg/d iron for 6 weeks separated by 8-week washout periods. Supplementation did not cause a rise in total oxidative DNA damage measured by GC-MS. However, a significant decrease occurred in levels of 8-oxo-7,8-dihydroguanine by ascorbate supplementation and B-hydroxymethyl uracil by both ascorbate? and ascorbate plus iron supplementation, relative to the pre-supplemental levels but not to the placebo group. In addition, levels of 5-hydroxymethyl hydantoin and B-hydroxy cytosine increased significantly, only relative to presupplementation, by ascorbate plus iron treatment. No compelling evidence for a pro-oxidant effect of ascorbate supplementation, in the presence or absence of iron, on DNA base damage was observed.