We have tested the hypothesis that moderate wine drinking can protect somatic cells against the DNA-damaging effect of hydrogen peroxide which is an endogenous source of reactive oxygen metabolites. In this preliminary investigation, four male volunteers were placed on a plantpolyphenol- free (PPF) diet to ensure that the wine provided was the only main source of plant phenolic compounds. After 48 h on the PPF diet the volunteers were required to consume 300 ml of red or white wine and blood samples collected 1, 3, 8 and 24 h post-consumption while still on a PPF diet. Plasma was isolated from the blood samples and stored frozen for subsequent assays. In the subsequent assays, fresh lymphocytes from each donor were incubated in their corresponding plasma from the various intervention time-points for 30 min. The capacity of the plasma to prevent damage to DNA in lymphocytes by hydrogen peroxide was assessed using the cytokinesis-block micronucleus technique. The data from this preliminary investigation indicated that there was a strong inhibition (>70%) of hydrogen peroxide-induced micronucleated cells by the plasma samples from the blood collected 1 h after consumption of wine as compared to plasma samples from blood immediately before the consumption of wine. This protective effect was apparent for both red and white wine although statistical significance (P = 0.0068) was achieved only in the white wine intervention. A higher degree of statistical significance (P = 0.0008) was achieved when the data for samples following the consumption of red and white wine were combined. There was no difference in the hydrogen-peroxide-induced micronucleated cell frequency when comparing results immediately before starting on the PPF diet, before consumption of wine, 8 h after or 24 h after wine consumption. The hydrogen peroxide-induced micronucleated cell frequency in cells incubated with plasma from blood collected 3 h after wine consumption was intermediate to that observed for plasma after 1 and 8 h after wine intake. The protective effect of plasma against DNA damage cannot be readily explained by the red wine content of phenolic compounds because results for red wine were similar to those for white wine even though white wine had a much lower level of total polyphenols. A possible explanation could be that alcohol, glycerol and ascorbate in wine together with specific wine phenolic compounds that are also equally present in red and white wine (e.g. hydroxycinnamates) may have contributed to the observed protection of nuclear material from hydrogen peroxide-derived reactive oxygen metabolites. This explanation is supported by data from in vitro experiments showing that incubation of lymphocytes either with alcohol or wine stripped of phenolic compounds resulted in a statistically significant (P < 0.05) dose-related reduction (up to 87% reduction) in hydrogen peroxide-induced micronucleated cell frequency.