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Type 2 diabetic subjects manifest both disordered insulin action and abnormalities in their pancreatic islet cells. Whether the latter represents a primary defect or is a consequence of the former is unknown. To examine the ␤-cell mass and function of islets from type 2 diabetic patients directly, we isolated islets from pancreata of type 2 diabetic cadaveric donors (n ‫؍‬ 14) and compared them with islets from normal donors (n ‫؍‬ 14) matched for age, BMI, and cold ischemia time. The total recovered islet mass from type 2 diabetic pancreata was significantly less than that from nondiabetic control subjects (256,260 islet equivalents [2,588 IEq/g pancreas] versus 597,569 islet equivalents [6,037 IEq/g pancreas]). Type 2 diabetic islets were also noted to be smaller on average, and histologically, islets from diabetic patients contained a higher proportion of glucagon-producing ␣-cells. In vitro study of islet function from diabetic patients revealed an abnormal glucosestimulated insulin release response in perifusion assays. In addition, in comparison with normal islets, an equivalent number of type 2 diabetic islets failed to reverse hyperglycemia when transplanted to immunodeficient diabetic mice. These results provide direct evidence for abnormalities in the islets of type 2 diabetic patients that may contribute to the pathogenesis of the disease. Diabetes 53: 624 -632, 2004

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