SummaryThe most effective dose and route of administration of alloxan were found to be 100 mg/kilo injected into the tail vein of the mouse. Fifty mice treated in this way all had blood sugar levels greater than 300 mg% 48 hours later. There were no mortalities.Fasting before the intraperitoneal injection of alloxan increased the mortality in mice without increasing the incidence of diabetes among the survivors.Mice resistant to the first injection of alloxan were not necessarily resistant to a second injection of the same dose.Alloxan hyperglycemia was not permanent in all mice, since the blood sugar levels of one-half of the survivors reverted to normal within 6 weeks.In the dosages administered epinephrine, cysteine, niacin and riboflavin did not give protection against the action of alloxan.