The diagnosis of functional hyperinsulinism would be made more frequently if the test for that condition were made more reliable and less confusing. It is proposed that the test be called “the glucose homeostasis test” rather than the currently used expression, “six hour glucose tolerance test” because the former term is actually what is determined. This will avoid confusion with the glucose tolerance test for diabetes which is done for a shorter period and which should be done with an entirely different technique. Diabetes is best demonstrated in venous blood; hyperinsulinism in arterial. The method of analysis in either case should give true blood sugar. A modification of the Folin-Wu method which has the advantages of rapidity, accuracy and ease of manipulation is suggested although any standard procedure for true blood glucose may be used.