A survey of thyroid function in 95 patients with primary biliary cirrhosis revealed the presence of thyroid antibodies in 24 females and 1 male. Thirteen (52%) of this thyroid antibody positive group (all female) had biochemical evidence of thyroid disease: 8 (32%) were hypothyroid (7 of whom showed signs of myxedema), 2 had elevated thyroid stimulating hormone (TSH) levels, and 3 had abnormal responses to stimulation with thyrotropin releasing hormone (TRH). In contrast, only 3 (4%) of the thyroid antibody negative patients had reduced serum thyroxine (T4) levels and none were clinically hypothyroid. Evidence of an increase in thyroid hormone binding, as reported by other workers, was not found, and both the resin uptake of radioactive triiodothyronine and the free thyroxine indices were normal in both groups. The presence of thyroid antibodies showed a highly significant association with lacrimal gland dysfunction but not with liver histologic staging or liver function tests.