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