In an attempt to define the pancreatic B cell function in the elderly, we subjected 88 non-obese individuals (aged between 21 and 88) to an oral glucose tolerance test (OGTT), a simple glucagon test (SGT) and OGTT-glucagon test, in which the plasma glucose, insulin and serum C-peptide (CPR) were measured. We investigated heterogeneity in glucose intolerance in the elderly and its relationship to atherosclerosis. In the OGTT and SGT test, the insulin responses (SIRI/SPG ratios) for normal, borderline and DM1 (fasting plasma glucose less than 140 mg/dl and 2 h-PG greater than or equal to 200 mg/dl) groups of the elderly (60 and above) were not significantly different from those for normal group of young and middle-aged (below 60) and were significantly higher for elderly group than for the young and middle-aged group in each glucose tolerance group. But the insulin responses for the DM2 (fasting plasma glucose greater than or equal to 140 mg/dl and 2 h-PG greater than or equal to 200 mg/dl) group of the elderly were not significantly different from those for the DM1 and DM2 groups of young and middle-aged. The insulin responses of normal, borderline and DM1 groups of the elderly with atherosclerosis were significantly higher than those of the comparable groups without atherosclerosis, while the insulin responses of the borderline and DM1 groups of the elderly with atherosclerosis were similar to those of the control group of the young. In the OGTT-glucagon test, there were no differences in the insulin response or serum CPR response among the normal, borderline and DM1 groups of the elderly, and these responses were significantly higher for the elderly group than the for young and middle-aged group in each glucose tolerance group. But these responses for the DM2 group of the elderly were not significantly different from those for the DM1 and DM2 groups of the young and middle-aged. These results indicate that the pancreatic B cell function of the normal group in the elderly remains favorable while mildly impaired glucose tolerance was exhibited by the borderline and DM1 groups, who are comparable with the normal group of the young and middle-aged. But this function was clearly reduced in the DM2 group of the elderly. These findings suggest that there is a subgroup in the elderly, which has clinically evident atherosclerosis, mild glucose intolerance and high insulin response. Their pancreatic B cell function remains favorable.