The sulphur dioxide released by aldose bisulphite addition compounds and their amine derivatives has been measured by the methods of Monier-Williams and Adams and Garber, and by direct iodine titration in acid solution. Bisulphite has been shown to react with glucosone, glycerosone, reductone, 3-deoxy-glucosone, and dehydroascorbic acid and crystalline addition compounds have been isolated from dehydroascorbic acid and glycerosone.