That a decreased carbohydrate tolerance accompanies acromegaly was conclusively shown by Davidoff and Cushing.1 In view of their observations it is not surprising to find the incidence of diabetes mellitus high in this condition. John2 reported three cases of this kind, in two of which the onset of acromegaly preceded the onset of diabetes. The fact that pituitary extract has an antagonistic action to insulin3 has brought up the question of whether the diabetes is a true diabetes or the result of an interference with the normal action of insulin. In some cases it would seem that there is a relative, rather than a true, pancreatic deficiency. In others, however, there is little doubt that the diabetes is a true diabetes mellitus, the acromegaly possibly being the original factor in causing the diabetes. Joslin4 pointed out that the chromophilic cells of the pituitary exert a partially controlling influence on the