Abnormalities in the electrophoretic patterns of plasma proteins in rheumatoid arthritis have been described by various workers. With few exceptions an increase in the relative concentration of a,-, a2-, and y-globulin and of fibrinogen and lowering of the albumin concentration have been observed and have been associated consistently with activity of the disease (1-15). Olhagen (4, 10) and Svartz and Olhagen (8) ascribed a possible prognostic significance to isolated elevation of a-or y-globulin. They suggested that an elevation of the a-globulins without an increase in the y-fraction, often noted in acute cases, indicated a tendency to more rapid healing, whereas a high y-globulin with low a-globulins represented a poor prognosis. Wallis (13) described a "T component" in three patients with active rheumatoid arthritis. A protein with a similar electrophoretic mobility, y'-globulin, was noted by Paul and Routh (14) in normal sera. These authors observed a small decrease of this fraction in the sera of seven patients with rheumatoid spondylitis but found no change in 27 patients with generalized rheumatoid arthritis. Recently, Laurell (16) and Mehl and Golden (17) have demonstrated the occurrence of small amounts of two proteins with isoelectric pH values lower than that of serum albumin when electrophoresis was performed in acetate buffer of pH 4.5. The concentration of one component, which at pH 8.6 in diethylbarbiturate migrates with a mobility of the a2-globulin, was considerably increased in sera from patients with rheumatoid arthritis (17) and disappeared on treatment with cortisone (16).