As the study of postoperative hypoglycemia is still a subject of interest to both surgeon and internist, we consider the following study worthy of report. The work is unavoidably incomplete, and there are only a few cases. However, the method of investigation is new, and the results obtained by its use give infinitely greater understanding of the significant changes in carbohydrate metabolism than does the older method of studying only the whole blood sugar. This method is offered to those who care to study the condition further, with the hope that it will be employed, and with the belief that the results will be of greater physiologic significance than those obtained by any other of the present methods. The method was devised by one of us (L. F.) for the study of insulin reactions.1 It is simple and can be carried out in any laboratory or well equipped office.