Mononuclear cells (MNC) from the blood of patients with autoimmune thyroiditis cannot be stimulated in vitro with the autoantigen thyroglobulin (Tg). However, when Tg was coupled with a solid matrix, MNC from 13 of 19 patients tested responded to this insolubilized Tg (i-Tg) by generating cells which produced IgG anti-Tg antibodies, as demonstrated in a "spot ELISA". This response was specific not only in the assay phase but also in the induction phase, because 1) cultures with insolubilized ovalbumin, bovine Tg, or porcine Tg were negative, and 2) i-Tg did not induce polyclonal IgG production. Generation of anti-Tg-producing cells was completely abrogated when free Tg was added to i-Tg cultures. Stimulation with i-Tg after separation of T and non-T MNC revealed that: 1) the response was independent of T cells; 2) in three of the six patients whose MNC did not respond, removal of T cells did result in anti-Tg production; 3) re-addition of the T cells--but not of irradiated T cells--abrogated the response in two of these three patients; and 4) preincubation of monocytes with i-Tg resulted in suboptimal anti-Tg production. These findings indicate that B cells from patients with autoimmune thyroiditis can be specifically stimulated with Tg coupled with a solid matrix, resulting in generation of anti-Tg-producing cells. The essence of this mode of presenting the antigen would appear to be the cross-linkage of surface immunoglobulin. The response was T cell-independent; in some patients, however, the presence of a radiosensitive suppressor T cell population can be demonstrated.