Although there has been extensive study of the changes in the peripheral vessels of the systemic circulation when affected by disease either primarily or secondarily, medical literature contains relatively few references to diseases of the peripheral pulmonary vessels. By roentgenologic examination, there is available a window through which one may view the pulmonary circulation in a manner which cannot be utilized in the study of the blood vessels of the rest of the body. It would seem useful, then, to review our knowledge of the conditions which may affect the small vessels of the lung and examine the pathologic and roentgenologic manifestations of them. In an excellent series of monographs, Brenner1has indicated that the arterioles, capillaries and venules of the lung may be subject to degenerative, infectious and neoplastic diseases similar to those encountered in the peripheral vessels of the systemic circulation, but accompanied by entirely dissimilar clinical