Light and electron microscopic examination of organs of rats rendered hyperglycemic with streptozotocin revealed the following: (1) rapid degranulation of beta cells without necrosis; (2) development of cataracts in four months after injection of 65 mg. per kilogram of the drug; (3) accumulation of glycogen in the proximal convoluted tubules of the kidney after 65 mg. per kilogram; (4) lesions in the exocrine cells of the pancreas after 100 mg. per kilogram; and (5) persistence of small, possibly secretory, granules in the Golgi zone of beta cells in diabetic rats. The significance of these findings is discussed.