Sixty six patients with Graves disease were followed up for the presence of TSAb at intervals of 4 to 12 weeks. Three different assays, the competitive TSH membrane-receptor assay (MRA), the cAMP-assay and the colloid droplet assay (CD) were used in parallel for demonstration of the antibody. In 17 of the patients TSAb was demonstrable also during remissions. 11 of these patients relapsed within a year. TSAb-positivity decline 1 to 4 months after 131I treatment. In case of persisting TSAb positivity 131I therapy or surgery should be given preference to thyrostatic medication. In gravidae followed up for TSAb, positivity not only persisted throughout pregnancy but even increased during the last trimester. After delivery all patients relapsed. One of the gravidae died of pregnancy toxicosis, the infant of another woman was thyrotoxic at birth. In pregnant women who have Graves disease and are positive for TSAb, thyrostatic or surgical treatment is recommended after the 2nd trimester even in cases of minor severity.