Serum precipitin reactions in Hashimoto's thyroiditis.

Sera from certain patients with Hashimoto's disease or a related condition contain a non-precipitating antithyroglobulin which produces in double-diffusion tests with thyroglobulin a line of clearing in the agar. Two such sera are described. Other sera from examples of the disease give negative precipitin tests with thyroglobulin but combine with sera containing ;clear line', non-precipitating antithyroglobulin to give a positive precipitin test. The serum from 15 out of 26 precipitin-negative cases of Hashimoto's disease showed this latent property. Eight of the 15 were tested by the tanned red cell technique and showed substantial titres of antithyroglobulin.