Tiselius fractionation of plasma proteins was performed on 27 patients with subacute (granulomatous) thyroiditis. In 21 there was a significant elevation of the [alpha]2-globulin level and in 18 of these 21 there was a significant elevation of the fibrinogen level. Other findings . of the fractionation of plasma proteins in subacute thyroiditis were: a decrease in the level of plasma albumin in 16 patients, and an elevation in the level of a1-globulin in 5, of beta-globulin in 2, of gamma-globulin in 12, and of fibrinogen in 19. In only 6 of 55 patients with Hashimoto''s disease, and in none of 30 patients with nontoxic adenomatous goiter were high values obtained for [alpha]2-globulin. In 6 of 35 patients with struma lymphomatosa the fibrinogen values were elevated. The erythrocyte sedimentation rate was increased in 18 of .20 patients in whom it was determined. The rate was elevated in 15 of 16 patients who had a high level of [alpha]2-globulin. The increase in the level of [alpha]2-globulin probably is largely due to the catabolic effect of the inflammation on thyroidal and, especially, on extrathyroidal tissues. This elevation was less likely to occur in patients who were less febrile, especially in those in whom only one lobe of the thyroid was affected. The diagnostic value of this test is largely limited to those patients in whom the clinical picture is more typical. Furthermore, an elevated level of plasma [alpha]2-globulin is a nonspecific finding, occurring in a number of other diseases, including other inflammations. It is our belief that a high value for [alpha]2-globulin, like the increased erythrocyte sedimentation rate and low thyroidal radioiodine uptake, is a useful finding only when correlated with the clinical picture. The diagnosis of subacute thyroiditis still is best made on a clinical basis, i.e., history, physical findings, response to prednisone or cortisone, and eventual disappearance of the goiter.