Abstract:A five‐hour oral glucose tolerance test and simultaneous determinations of serum immunoreactive insulin were performed on 20 male and 20 female elderly nondiabetic subjects whose ages ranged from 68 to 91 years. Results of the glucose tolerance test were abnormal in 29 of the 40 subjects (72.5 per cent) according to accepted standards for young and middle‐aged normal adults. The abnormalities were similar to those found in cases of diabetes mellitus in young adults. The response to glucose stimulation in these elderly subjects was delayed and less efficient than normal. Significant differences were observed with respect to both serum glucose and immunoreactive insulin, the females exhibiting higher levels than the males. Regression analysis showed no immunoreactive insulin in the serum when the glucose level was less than 50 mg per 100