The aim of this study was to determine the effects of antioxidants, including alpha-ketoacids (alpha-ketoglutarate and pyruvate), lactate and glutamate/malate combination, against oxidative stress on rat spermatozoa. Our results showed that H(2)O(2) (250 micromol L(-1))-induced damages, such as impaired motility, adenosine triphosphate (ATP) depletion, inhibition of sperm protein phosphorylation, reduced acrosome reaction and decreased viability, could be significantly prevented by incubation of the spermatozoa with alpha-ketoglutarate (4 mmol L(-1)) or pyruvate (4 mmol L(-1)). Without exogenous H(2)O(2) in the medium, the addition of pyruvate (4 mmol L(-1)) significantly increased the superoxide anion (O(2)(-).) level in sperm suspension (P < or = 0.01), whereas the addition of alpha-ketoglutarate (4 mmol L(-1)) and lactate (4 mmol L(-1)) significantly enhanced tyrosine-phosphorylated proteins with the size of 95 kDa (P < or = 0.04). At the same time, alpha-ketoglutarate, pyruvate, lactate, glutamate and malate supplemented in media can be used as important energy sources and supply ATP for sperm motility. In conclusion, the present results show that alpha-ketoacids could be effective antioxidants for protecting rat spermatozoa from H(2)O(2) attack and could be effective components to improve the antioxidant capacity of Biggers, Whitten and Whittingham media.