A lowered level of serum albumin and an increased PBI-BEI difference have diagnostic value in Hashimoto''s thyroiditis. The zinc sulfate concentration and the erythrocyte sedimentation rate were abnormally high in a large proportion of 101 patients having Hashimoto''s thyroiditis, but also in nearly as high a proportion of 39 euthyroid patients with nodular goiters. For this reason the practical diagnostic usefulness of these two tests is negligible. When the zinc sulfate, PBI-BEI difference, alpha-1-globulin, and alpha-2-globulin tests were considered as a group, one or more gave abnormal results in 97 per cent of patients with thyroiditis and in 72 per cent of euthyroid patients with adenoma-tous goiter. This surprising proportion of abnormal values in the cases of euthyroid adenomatous goiter makes the use of such combinations of tests of relatively little value in the diagnosis of Hashimoto''s thyroiditis. It is not known why so many of these laboratory findings are abnormal in patients with Hashimoto''s thyroiditis and in an equally impressive, although significantly smaller proportion, of euthyroid patients with adenomatous goiters.