TSH receptor antibodies (TRAb) measured by the TBI residual assay (TBIr) were studied in 3 groups of Graves disease patients, as follows: 54 non treated cases (Group 1), 20 cases under methimazol treatment (Group 2) and 23 patients who were euthyroid after one year of methimazol treatment (Group 3), in order to evaluate the usefulness of TBIr as a recurrence index in Graves disease following antithyroid drug treatment. In group 1, TBIr was positive in 77.7% (45/54) of the cases. In group 2: 45% (9/20) had positive values for TBIr, all of which had a recurrence of disease during the year following the suppression of the treatment. In group 3, 69.5% patients (16/23) were TBIr positive. In 75% (12/16) of them the abnormally high values of TBIr predicted the recurrence, while 71.43% (5/7) of the patients, TBIr negatives, continued the remission 12 months later. By comparing the TBIr values before and after treatment in the group 3 patients, different possibilities were observed: a) TBIr persistently elevated: 52.17% (12/23). The 83.3% (10/12) had a recurrence before 6 months following treatment termination. b) TBIr, initially elevated, but later showing 50% decrease or negative values: 26.09% (6/23). Every patient was euthyroid one year after the treatment ended. c) TBIr persistently negative: 13.04% (3/23). Two of them had recurrence of their disease. d) TBIr negative which changed later to positive: 8.70% (2/23). Both presented a recurrence. In accordance with these results, we believe that abnormally high TBIr values before or after treatment is a useful recurrence index.(ABSTRACT TRUNCATED AT 250 WORDS)