THE structure and properties of dehydroascorbic acid are to a certain extent similar to those of alloxan, and both the substances are diabetogenic in rats1,2. It was previously reported by Bhattacharya, Robson and Stewart3 that dehydroascorbic acid causes a precipitous but temporary fall in the reduced glutathione content of rat liver. Their results suggested that the fall in reduced glutathione was not due to oxidation but due to a complex formation between the sulphydryl group of glutathione and dehydroascorbic acid. Hexokinase is an enzyme the activity of which probably depends on the presence of free sulphydryl group(s)4,5. It seemed desirable, therefore, to study the effect of dehydroascorbic acid on the hexokinase activity of rat liver homogenate. Although Griffiths6 reported that cysteine is capable of releasing the inhibition of muscle hexokinase by alloxan, in view of the results obtained with dehydroascorbic acid it was decided to study the effect of alloxan and cysteine on liver hexokinase.