Amiodarone iodine induced thyrotoxicosis occurs frequently in patients residing in areas of mild iodine deficiency and in patients with preexisting goiter. Drug therapy of the hyperthyroidism is often unsuccessful. Twenty-three patients with amiodarone induced thyrotoxicosis were either not treated, treated with 40 mg methimazole daily or with methimazole and 1 gm potassium perchlorate daily for up to 40 days and then with methimazole alone. Thyrotoxicosis was more likely to spontaneously remit in patients without goiter. Therapy with methimazole alone was unsuccessful in inducing euthyroidism in 5 patients with goiter. However, combined therapy with methimazole and potassium perchlorate rapidly alleviated hyperthyroidism in almost all patients with goiter. This drug combination is successful because perchlorate inhibits the active transport of iodine into the thyroid and methimazole blocks the intrathyroidal synthesis of thyroid hormones.