Berry extracts possess antioxidant activity in cell free systems, whereas cell culture and animal experimental systems have produced mixed outcomes. Our aim was to investigate the effects of blackcurrant juice and specifically blackcurrant anthocyanins on the steady state level of oxidative DNA damage in mononuclear blood cells (MNBC) of humans, determined as strand breaks (SB) as well as endonuclease III (Endo III) and formamidopyrimidine DNA glycosylase (Fpg) sensitive sites by the comet assay. Fifty-seven healthy humans completed a 3-week controlled parallel intervention study with three groups randomized to supplementation with blackcurrant juice, anthocyanin drink, or a control drink. The daily doses ranged from 475 to 1000ml/d according to body weight (mean anthocyanin intakes in blackcurrant juice and anthocyanin drink groups were 397 and 365g/d, respectively) and they were ingested during three daily meals while all volunteers were on the same strictly controlled low-flavonoid diet. Fasting venous blood samples were obtained at baseline and after 3-week of supplementation. The baseline level of oxidative DNA damage was low (e.g. less than 200 Fpg lesions per diploid cell). Fpg sensitive sites increased during the intervention within the blackcurrant juice group, whereas there were no differences between treatments in any of the DNA damage markers. In conclusion, this study shows that even large amounts of dietary antioxidants did not decrease the already low steady state levels of oxidative DNA damage in healthy adequately nourished humans.