Clinical usefulness of thyroid-stimulating antibodies (TSab) and TSH-binding inhibitor immunoglobulins (TBII) for predicting the prognosis in patients with Graves' disease after cessation of antithyroid drug treatment was evaluated, and compared with that of T3 suppression test and goitre size. Among 46 patients who had been euthyroid on a maintenance dose of antithyroid drugs for at least one year and had discontinued taking medicine, 16 relapsed within one year (group 1), 7 relapsed later than 1 year (group 2), and 23 patients remained in remission for more than 1 year (group 3). Incidence of TSab, TBII, T3 nonsuppressibility and large goitre (transverse diameter longer than means of the values for the 46 patients: greater than or equal to 4.36 cm in females; greater than or equal to 4.74 cm in males) determined at the time of discontinuation of treatment was 87.5% (14/16), 56.3% (9/16), 78.6% (11/14) and 81.3% (13/16) in group 1; 66.7% (4/6), 28.6% (2/7), 50.0% (3/6), and 57.1% (4/7) in group 2, and 56.5% (13/23), 24.1% (5/23), 35.7% (8/23), and 26.1% (6/23) in group 3, respectively. All relapsed patients showed remarkable increases in both TSab and TBII activities at the time of relapse. High incidence of TSab in patients remaining in remission suggests that a reduced functional reserve of the thyroid, probably owing to destructive changes and/or shrinkage of the gland, may cause impaired responses to TSab and is involved in the cause of remission. Development of blocking type of TBII was not considered to be a cause of remission. Remission was predictable in all patients with any two of the indices such as negative TSab, positive T3 suppressibility, and small goitre.