We presented a simple and sensitive test for thyroid hormone autoantibodies. The normal range for T4 and T3 autoantibodies in Thai people considering mean +/- 3 S.D. were 1.8-9.4 per cent and 3.1-8.6 per cent, respectively. Although positive low titer of thyroid hormone autoantibodies had almost no interference of thyroid hormone levels, high titer might cause great interference. This method can be used for screening patients who have unexpectably high levels of serum T4, T3 or discrepancy between thyroid hormone levels and clinical findings.