In 1942 together with Dr. Paul Klemperer we1employed the term "diffuse collagen disease" to indicate that in disseminated lupus erythematosus and in diffuse scleroderma, the basic morphologic changes were found in the connective tissues. Similar but less conspicuous changes in the connective tissues are observed also in rheumatic fever, periarteritis nodosa, rheumatoid arthritis, thromboangiitis obliterans and serum sickness. It must be emphasized that in each of these diseases this collagen degeneration may lead to conspicuous alterations in the walls and lumens of blood vessels, in the endocardium, pericardium and pleura, in the articular and periarticular tissues and in the dispersed connective tissues (mediastinum, retroperitoneum and subcutaneous tissues). Thus, in all the diseases of this group, one may encounter clinical evidences of vascular involvement, pericarditis, pleuritis and arthritis. In recent years much emphasis has been placed on the fact that fibrinoid degeneration of collagen and the various vascular and