It is intended to provide a noninvasive method of conveniently detecting mild impaired glucose tolerance and/or insulin hyposecretion at the early stage with the use of an enzyme. Namely, mild impaired glucose tolerance and/or hyposecretion at the early stage are detected by quantifying myoinositol secreted into the urine before loading glucose and after loading glucose for a definite period of time with the use of a reagent and comparing the increase (or the increase ratio) in the myoinositol content thus measured with a characteristic level which has been preliminarily determined in normal subjects.