In three groups of persons, 1) 19 healthy individuals, 2) nine patients with asymptomatic diabetes mellitus, and 3) eight patients with clinical diabetes mellitus, the plasma c1earance rates (CR) of cortisol and corticosterone were estimated simultaneously by means of an intravenous infusion of a tracer dose of both tritium labeled hormones at a constant rate until a steady state was reached (constant infusion technique). The plasma concentrations (C) of each of the two endogenous hormones were measured separately with a fluorometric method. The plasma production rates (PR) of both hormones were then calculated and correlated to body surface. Compared to the values in the normal group the mean PR's of cortisol in both diabetic groups were not lignificantly elevated statistically though they were augmented. The elevations of the PR's of corticosterone were significant in Group 2 and highly significant in Group 3. Besides the gluconeogenetic action of the two augmented hormones, their action on potassium excretion is discussed. It is also pointed out that the possible depletion of potassium in the beta cells of the pancreas could be related to the pathological insulin secretion and the impaired carbohydrate tolerance in asymptomatic and c1inical diabetes mellitus.Horm. Metab. Res. 2: 357-363 (1970) K e y -W 0 r d s: Dißbetes -Cortisol -CorticosteroneProduction Rates.