Purpose.- Literature data regarding lactate effects towards oxidative stress induced by exercise are conflicting, particularly in vivo, as lactate effects may be hardly dissociated from the concomitant acidosis. This study was aimed at assessing pro- and antioxidant effects of various lactate concentrations (1, 10, 15, 30, 60 mM), using two methods.Methods and results.- Evaluation of malondialdehyde (MDA), a marker of lipoperoxidation induced by iron supplementation in hepatocyte culture medium was first done. Quantification of free radical production using spin-trapping electron paramagnetic resonance spectroscopy was then done. Results clearly demonstrated an antioxidant effect of lactate ions in vitro, which was dose-dependent. MDA was significantly decreased with 15 mM lactate. As well, superoxide anion was significantly scavenged for all lactate concentrations, after the latter had been dissolved in either aqueous or plasmatic solution.Conclusion.- This study demonstrate that lactate has antioxidant effects in vitro.Introduction.- Les effets du lactate face au stress oxydatif de l'exercice sont controverses, notamment in vivo car difficiles a dissocier des effets de l'acidose concomitante. Nous avons donc teste l'effet de l'ion lactate sur la production de radicaux libres in vitro.Methode et resultats.- Deux methodes ont ete utilisees: d'une part le dosage par chromatographie du malondialdehyde, marqueur de la lipoperoxydation d'hepatocytes de rats en culture et, d'autre part, la resonance paramagnetique electronique, qui permet de quantifier la production de radicaux libres, en presence du lactate dissous soit en solution aqueuse soit plasmatique. On observe dans le premier cas une inhibition significative de la production de malondialdehyde a partir de 15 mM de lactate et un pourcentage de piegeage significatif de l'anion superoxyde pour toutes les concentrations de lactate dissous en solution aqueuse et plasmatique.Conclusion.- Cette etude montre que le lactate exerce in vitro un effet antioxydant.