Lactobacillus acidophilus CUL21 (NCIMB 30156) Lactobacillus acidophilus CUL60 (NCIMB 30157) Bifidobacterium bifidum CUL20 (NCIMB 30153) Bifidobacterium animalis subsp. lactis CUL34 (NCIMB 30172) and will be administered orally, twice a day during meals, for 6 months. Samples of blood (for serum and DNA)and, tears (Schirmer strips), nasal swabs and faeces will be collected at the first visit, before any treatment or within 4 weeks of anti-thyroid drug (ATD) therapy commenced by community physician. The same samples will be collected on the first occasion that euthyroidism has been restored on the usual block/replace or titration regimen used locally. The same samples will also be collected 6 months after cessation of treatment or at the point of relapse if that is sooner .