BACKGROUND: Type 2 diabetes (T2D) is characterized by impaired tissue sensitivity to insulin action (ie, insulin resistance) and impaired β-cell insulin secretion. Because obesity contributes importantly to the development of insulin resistance, we sought to determine whether insulin secretory defects would predominate in non-obese compared to obese T2D. METHODS: We measured β-cell function and secretory capacity using the glucose-potentiated arginine test in T2D subjects early in the disease course classified as non-obese (BMI