The clinical usefulness of commercially prepared haemagglutination kits for thyroperoxidase (TPO) antibody and thyroglobulin (TG) antibody was evaluated in 145 consecutive Jamaicans with Graves' disease. Sixty two (43%) of the patients were newly diagnosed, 12 (8%) were in remission and 71 (49%) had relapsed. Sera from 65 (45%) patients were positive for thyroid antibodies. The TPO antibodies were found in 43% (63/145), thyroglobulin antibodies in 12% (17/145) fifteen (10%) patients had both anti-TPO and TG antibodies. Similar prevalences of TPO antibody were found in newly diagnosed patients and those who had relapsed (44% v. 41%) but the prevalence in the patients in remission was significantly higher (75%; X2 = 4.8, P < 0.05). The prevalence of TPO antibody increased significantly with age at onset before age 35 years compared to later onset (56% v. 32%; X2 = 8.09, P < 0.005). The presence of both TPO antibody (64% v. 31%; X2 = 13.1, P < 0.001) and TG antibody (22% v. 6%; X2 = 8.8, P < 0.005) correlated positively with Graves' ophthalmopathy. Neither of the tests was adequately sensitive in detecting GD in Jamaicans but we recommend testing for TPO antibody without TG antibody as a cost-effective approach. The presence and titres of TPO antibody and TG antibody do not correlate with disease activity and are not reliable enough for monitoring antithyroid drug therapy in GD. There is a need for antibody tests which are efficacious in diagnosing and monitoring antithyroid drug therapy in GD, and suitable for use in developing countries.