The chemical reactivity of various alpha-keto acid anions (beta-hydroxypyruvate, beta-phenylpyruvate, 2-ketobutyrate and 2-ketoglutarate) with hydrogen peroxide (H2O2) was investigated at physiological pH (7.4) and a temperature of 25 degrees C. The initial concentration of the alpha-keto acid anions was kept constant at 1.00 mM whilst that of added H2O2 was varied from 0.25 to 1.00 mM, and the rate and extent of these reactions was evaluated using 1H NMR spectroscopy. At all H2O2 concentrations utilised, the order of reactivity of the alpha-keto acid anions was beta-hydroxypyruvate > beta-phenylpyruvate > 2-ketobutyrate > 2-ketoglutarate. The results obtained are in agreement with a proposed mechanism for these reactions, involving nucleophilic attack of the mono-deprotonated peroxide species (HO2-) at the C-2 carbonyl group carbon centre. The antioxidant capacity of such alpha-keto acids is discussed in terms of their potential use as therapeutic agents in clinical conditions where H2O2 has been shown to play a critical role in the disease process, i.e., those involving 'oxidative stress'.