The blood-sugar conc. of the normal owl varied from 200 to 350 mg. %. The glucose tolerance curve of the normal owl was prolonged and typical of the mild diabetic state while the insulin response was similar to that observed in other spp. Fasting induced the accumulation of acetone bodies in the blood. Pancreatectomy resulted in hyperglycemia to levels as high as 1200 mg. %, a loss of appetite, an increased susceptibility to fasting ketosis and death irrespective of whether or not insulin was administered.