The BB/Wor rat develops spontaneous insulin dependent diabetes mellitus (DM) and lymphocytic thyroiditis (LT). We have recently demonstrated that although the incidence of spontaneous DM is relatively constant among different inbred BB/Wor sublines the incidence of LT is extremely variable. Experimental LT can be induced in some animal species by immunization with thyroglobulin (Tg). The differences in susceptibility of Tg induced LT between a high incidence LT subline (NB) and a low incidence subline (BB) were determined after immunization with Tg obtained from Wistar rat thyroids. Immunization was accomplished using 0.6 mg Tg in complete Freund's adjuvant (FA) or FA alone at 30 and 37 days. Since spontaneous LT rarely occurs before age 75 days, rats were sacrificed at age 65 days to specifically study Tg induced LT. Immunization with Tg induced LT in the NB subline but not in the BB subline. Anti-Tg antibody (Ab) titers, T4-Ab and T3-Ab were all increased in both Tg immunized sublines but were significantly higher in Tg immunized NB rats than in Tg immunized BB rats. The increase in T4-Ab or T3-Ab resulted in factitiously low serum T4 and T3 values when a single Ab technique with polyethylene glycol (PEG) precipitation was used in the RIA. There was a dissociation in the incidence of Tg induced LT and Ab production. Although Tg immunization failed to induce LT in the BB subline, anti-Tg Ab were significantly elevated as well as both T4-Ab and T3-Ab, suggesting that anti-Tg Ab titers per se are not tightly correlated with the occurrence of LT.(ABSTRACT TRUNCATED AT 250 WORDS)