Rats given streptozotocin showed varying degrees of glucose intolerance, ranging from mild to overt symptoms of diabetes mellitus. After being deprived of food overnight, both mild and overt diabetics consumed more food than controls did during 5-hr or 7-hr feeding tests. All animals ate large amounts of food during the first hour of the tests, but both groups of diabetics began to eat again sooner than controls did. Rats demonstrating the greatest degree of glucose intolerance before the test ate the most during the test. These and other findings suggest that feeding by diabetic rats after an overnight fast is an inverse function of their residual capacity for glucose utilization, which occurs despite elevations in blood glucose levels, and is not simply a compensatory response to glucose loss in urine. A modified glucostatic hypothesis is proposed in which insulin may normally promote satiety by influencing peripheral metabolism and making ingested calories utilizable.