KLEMPERER, Pollack, and Baehr1 in 1941 described the basic pathology of disseminated lupus erythematosus as a systemic alteration of the extracellular elements of the connective tissue. This alteration consisted mainly in a mucoid and fibrinoid degeneration of the ground substance and the collagen fibers. They later pointed out2 that there were other diseases that exhibited similar widespread alterations in connective tissue, and that there might be pathogenetic significance in the fact that these diseases all had a common anatomic site: that they were, in fact, diseases of the connective tissue system. They were designated as the "collagen diseases," and the list has grown from the original disseminated lupus erythematosus and generalized scleroderma to include rheumatic fever, rheumatoid arthritis, dermatomyositis, periarteritis nodosa, and serum sickness. The authors were quick to point out that by linking these obviously heterogeneous diseases together they did not mean to