Abstract Glucose tolerance tests were performed on 7 patients with dystrophia myotonica and on 6 controls. In each patient the test was performed once with 50 Gm. of glucose and once with 100 Gm., and in each test both capillary and venous blood were examined. The fasting blood sugars and the glucose tolerance curves were normal in all patients; no glycosuria was evident. Composite glucose tolerance curves showed slight differences between patients and controls: (1) The glucose tolerance curves were slightly flatter in the patients than in the controls. (2) The composite curves for 100 Gm. tended to remain elevated in the patients at the second and third hours, especially in the capillary blood. (3) The capillary-venous differences remained slightly higher in patients than in controls receiving 100 Gm. of glucose. None of these differences was great enough to be statistically significant, and no correlation was found between variations in response to the tests and the severity of the disease. Since marked dysfunction of the islands of Langerhans, the anterior pituitary gland, or the adrenal cortex is usually reflected in the fasting blood sugar and in the sugar tolerance curve, the results obtained furnish some evidence against a marked involvement of these endocrine glands. The removal of glucose from the capillary blood by the tissues, as indicated by the capillary-venous differences, also appears normal. It may be concluded that the mechanisms controlling the disposal of ingested glucose in dystrophia myotonica are normal.