Hypoglycaemic fractions of A. cepa Linn (onion) have been separated. After 7 days treatment, the more active hypoglycaemic fraction was about half as active as Phenformin in lowering the fasting blood sugar of alloxan-diabetic rabbits. Oral administration of the hypoglycaemic fraction to alloxan-diabetic rabbits improved their glucose tolerance also. Juice expressed residue of onion, when fed to diabetic patients along with their food, controlled the hyperglycaemia effectively.