The authors show, by an elaboration of Hartmann''s method, how the ami. of insulin produced in the body, or its equivalent effect on carbohydrate metabolism may be estimated, and how, by subtracting the calculated endogenous insulin from the total insulin requirement, an accurate estimate is obtained of the amt. of exogenous insulin required. It is possible, by the method employed, to estimate the physiologic activity of the liver, pancreas and other organs concerned with carbohydrate metabolism in terms of units of endogenous insulin, and to predict with considerable accuracy what the blood sugar conc. will be following the adm. of a definite amt. of glucose and an exactly calculated dose of insulin. Evidence is presented that the conception that 1 unit of insulin will metabolize 2 gms. of glucose is approximately correct. The authors discuss liver failure during coma and show how the breakdown of carbohydrate metabolism during coma due to depressed hepatic and pancreatic function may be expressed mathematically in terms of insulin deficit, and have indicated how this may be used as a prognostic aid and a guide to subsequent insulin dosage.