The denaturation of lens proteins as apparent by the generation of protein carbonyl in the presence of active oxygen and the prevention of such denaturation by pyruvate were studied. Active oxygen was generated by the action of xanthine oxidase on xanthine under aerobic conditions. Rat lens protein when incubated with xanthine and xanthine oxidase produced significant amounts of the carbonyl derivative. The formation of such carbonyl was substantially inhibited by pyruvate. In addition, the keto acid also was found to stimulate the utilization of glucose through HMP shunt, a mechanism known to transport reducing equivalents from glucose to peroxide. The results suggest that pyruvate exerts a beneficial effect in attenuating the age-related protein modifications and consequent physiological impairments. These studies are also considered useful from the therapeutic point of view.