A comparative study of high-dose (HD, carbimazole 60 mg plus thyroxine 100-150 micrograms daily) and titration-dose (TD) regimens of carbimazole was carried out in 70 patients with Graves' disease, the patients being assigned randomly to one or other regimen. The treatment was given for 1 year and follow-up was for 2 years after stopping treatment. In both groups, recurrence of hyperthyroidism occurred, most commonly during the first 6 months (35% of HD and 44% of TD). By 2 years after stopping treatment, recurrence had occurred in 50% of the HD and 66% of the TD group. The differences were not significant. Thyroid antibodies, serum thyroglobulin and pertechnetate uptake fell similarly in both groups during treatment. Cigarette smoking was similar in both the groups and did not influence the frequency of relapse. In both HD and TD groups, when relapsing patients were examined according to whether they relapsed early (within 6 months or less) or late it was found that those who relapsed late were, in respect of goitre size, pertechnetate uptake and presence of detectable plasma TSH, similar to the patients who did not relapse at all. In conclusion, the changes in the measured variables and the progress of the patients was similar whether treated by the HD or TD regimen.