In a group of adult Seneca Indians living in Western New York, 14 per cent were discovered to have previously diagnosed diabetes, and 20 per cent of the remainder had a plasma glucose of 200 mg. per 100 ml. or greater one hour after oral carbohydrate. This report describes the glucose and insulin responses to oral carbohydrate in fifty of these subjects who were not previously known to have diabetes during initial testing. On the basis of the results of a two-hour oral glucose tolerance test, forty-six subjects were classified into “diabetic” or “normal” categories. Four persons formed an intermediate group. The diabetics differed from the normals in that (1) they were older and more obese, though even the normal population was significantly obese, and (2) the mean fasting plasma insulin level was three times greater and the insulin response to oral glucose two and one-half times greater than in normals. When diabetics were subdivided on the basis of obesity or degree of glucose intolerance, no significant differences in insulin secretion could be detected. A group of diabetic subjects with a degree of obesity comparable to that of normal subjects still demonstrated two-fold increases in both fasting and postglucose insulin levels. The elevated insulin levels of diabetics can be explained only in part by co-existent obesity and suggest the presence of insulin resistance associated with diabetes in these Indians.