We aimed to establish and extend the characterization of murine models of thyroiditis and Graves' ophthalmopathy, induced by transfer of TSH receptor (TSHR) primed T cells. Experiments were performed in a different animal unit but using female BALB/cbyJico mice from the same supplier as previously. We report our findings together with a reevaluation of the earlier studies. In the first experiment, genetic immunization or TSHR fusion protein induced TSHR antibodies in all nine mice. Some of the antibodies functioned as thyroid-stimulating antibodies and/or TSH binding inhibiting Igs with two of seven mice having elevated T4. Thyroiditis and orbital changes were absent. Splenocyte transfer induced no immune response in naive BALB/cbyJico recipients. Subsequently genetic immunization or fusion protein-treated mice were maintained in either local or Brussels conditions (water, chow, and bedding). TSHR antibodies were induced in nine of nine Brussels (with decreased T4 in one of nine) but five of nine local mice. No thyroiditis or orbital changes were induced, but misleading fixation artefacts in extraocular muscles were noted. Nonspecific in vitro stimulation induced more CD-4+/IL-4+ cells in Brussels maintained. TSHR stimulation produced a significant increase in IL-4 secretion in six of nine local but one of seven Brussels mice. Thyroids from many TSHR-treated and control mice contained ectopic thymus. Our results confirm that thyroiditis is required for disease transfer but indicate the heterogeneity in TSHR-induced immune response in an inbred strain. Ectopic thymus can masquerade as thyroiditis, and care is required to avoid muscle artefacts. Because neither animal unit is pathogen free, microbial environment may contribute to determining TSHR-induced responses.