We investigated the incidence of thyroid auto-antibodies and their relationship to antigastric antibodies in 20 euthyroid patients with pernicious anaemia. To evaluate possible thyroid dysfunction we also measured total level of thyroid hormones (TT3 and TT4) and TSH in our patients. Histologic evidence of autoimmune atrophic gastritis and intestinal metaplasia was obtained in 15 patients. We found that it was surprisingly high incidence of thyroid auto-antibodies in patients with pernicious anaemia, particularly in the group with intestinal metaplasia (antithyreoglobulin antibodies 71% and antimicrosomal antibodies 100%). The incidence of antigastric antibodies in these patients was similar to that of those with significant antithyroid antibodies (16/18). Total triiodo thyronine and TSH were significantly higher in the patients with pernicious anaemia than in the control group (p less than 0.05), in the normal range. The results of our study suggest that this upset in immunological physiology is due to a more generalized defect in immune tolerance.