Sodium threonate (threonic acid) is a major breakdown product of ascorbic acid used as a food additive. It is formed in insignificant amounts from ascorbic acid used as a technological aid in the food industry. When administered orally to guinea-pigs (100 mg/kg body weight) for periods of 4 or 28 days, it produced a significant fall in the ascorbic acid concentration of certain organs but was without effect on other physiological and biochemical characteristics. The lifespan of scorbutic guinea-pigs was significantly reduced by dietary threonic acid (100 mg/kg body weight). The results indicate that threonic acid may modify the metabolism of ascorbic acid in guinea-pigs. Threonic acid is a normal component is aqeous humour and blood. Threonic acid is a substrate of L-threonate 3-dehydrogenase in ascorbate and aldarate metabolism pathway.