The role of stress proteins in the pathology of autoimmune thyroid disease (AITD) has aroused considerable controversy in recent years1. Thyroid cells in tissue culture are known to synthesise a range of stress proteins (hsp) in response to elevated temperatures or toxic chemicals2. Hsp70 over expression has been demonstrated in thyroid tissue from patients with Graves' disease3and intra-thyroidal T-cells from these patients can also be induced to expand in response to hsp70 from a variety of sources4. Unpublished data from our own laboratory shows that the incorporation of [3H] thymidine into peripheral lymphocytes from patients with AITD is also enhanced when these cells are cultured in the presence of stressed thyroid cells. However, in the same experiments, lymphoproliferation was also enhanced by PPD, a preparation rich in Mycobacterial hsp, which is a common immunogen in the population.