METHODS. A mixed stock of colored varieties of the albino rat was used. The selection of animals, care of the animal room, diet, post-operative care, and the technique of suprarenalectomy have been described in previous papers from this laboratory (Belding and Wyman, 1926; Wyman, 1928a). Approximately equal numbers of each sex were used in each experiment. No sex differences with respect to blood sugar were noted. Rats from three to six months old were selected for suprarenalectomy. Autoplastic cortical transplants were made by the technique of Jaffe and Plavska (1926) in young rats from one and a half to four months old. A description of the technique, of the results of the operation, and of the microscopic appearance of the transplants has been given in a previous paper (Wyman, 1928b). One point of technique seems worthy of note. In a series of 39 successful transplants made for this and for other studies the capsule was carefully stripped from one suprarenal gland which was transplanted in two pieces on the left side of the abdomen. The gland which was transplanted on the right side was cut into two pieces without removing the capsule. This was done with the idea that removal of the capsule might favor the growth of the transplant. It was found at autopsy that in 38 cases one or two large masses of cortical tissue had regenerated from the gland with the undisturbed capsule, while with the exception of five cases the gland without the capsule had completely disappeared. Evidently removal of the capsule is unfavorable to successful transplantation of the suprarenal. Blood sugar was determined by the ferricyanide micro-method of Folin (1928) using 0.05 cc. capillary pipettes of the type described by Folin for collection of blood samples. In a preliminary experimental series frequent excessively high blood sugar values were observed, for which no adequate explanation was at hand. By preparing the dilute tungstic acid and the