Vos X et al. - The prevalence of TBII-seronegativity in untreated patients with GH is 5·4% using a second generation assay. TBII-seronegative patients have biochemically less severe thyrotoxicosis and no Graves' orbitopathy. TBII-seronegative and TBII-seropositive patients apparently belong to the same population of GH, albeit the severity of the autoimmune attack is less in TBII-seronegative patients.