Preoperative management of treatment in thyrotoxicosis was investigated in a comparative study of carbimazole and propranolol in 41 consecutive patients collected during a 3-year period. The groups included 20 and 21 patients respectively, of equal sex and age distribution and of similar severity. The length of the preoperative treatment was significantly reduced in the propranolol pretreated patients (P greater than 0.001). Intraoperative blood loss, postoperative function with regard to the thyroid, parathyroids and vocal cords were similar in both groups. Three and two patients respectively had permanent hypothyroidism requiring thyroxin treatment. In patients with therapy compliance problems treatment with propranolol would entail a definite advantage, particularly in developing countries.