We have not found in the literature a report of an instance of permanent homoio or autotransplantation of the spleen, or of the probably closely related spleno and hemolymph glands. Spleen autotransplants with considerable difficulty as compared with thyroid, parathyroid, ovary, or adrenal cortex. This may be due to its complex anatomical structure. An instance of a permanent autotransplant has been observed. None of our attempts to homoiotransplant it were successful beyond the usual taking and persistence for 2 or 3 weeks, common to all homoiografts. The successful permanent subcutaneous autotransplantation had all the morphological characteristics of a fully differentiated and functionally active spleen. This method of transplantation would seem to offer a means of learning more of the normal development, regeneration, and function of this complex tissue.