HOMOLOGOUS transplantation of tissues and organs has been, on the whole, unsuccessful. Nevertheless, functionally useful homotransplants in man have been obtained with various tissues, such as the cornea, 1 blood vessels, 2 and skin. 3 These results are encouraging to the surgeon, since they suggest that more knowledge of the factors responsible for the destruction of homografts may enable him to apply the technic of homotransplantation to a wide variety of tissues and organs. The homologous transplantation of an entire lung has not been performed up to the present time either in lower animals or in man. The purpose of this investigation was twofold: (1) to determine whether homologous transplantation of a whole lung is feasible from the viewpoint of surgical technic, and (2) to ascertain the behavior of the transplanted lung with respect to its structure and function. Considerable difficulties were encountered in performing the operation of homotransplantation of