IN 1947, a technician who had rheumatoid arthritis and who worked in the laboratory of Dr. Harry Rose at Columbia University discovered that her own serum agglutinated excessively. Dr. Rose suggested that this serologic reaction might have been caused by the arthritis. Charles Ragan, a rheumatologist, pursued this suggestion and developed the sheep-cell agglutination test,^{1 , 2} which we know as a test for rheumatoid factor. For the first time, physicians had a key to the black box that was rheumatoid arthritis and could begin to study the immunologic abnormalities in patients with the disease. The classification of patients could also begin; . . .