Combined antithyroid-thyroid drug therapy is not recommended for the pregnant hyperthyroid because: a) the least possible dose of anti-thyroid drug and a full dose of exogenous thyroid are mutually exclusive objectives; b) combined therapy increases the fetus's exposure to antithyroid drug; c) added thyroid changes the source but not the quantity of hormone in the maternal circulation; d) euthyroid mothers do give birth to goitrous or athyrotic cretins, suggesting that normal concentrations of maternal thyroid do not protect the fetus; e) combined therapy complicates treatment unnecessarily; f) management with antithyroid drug alone is satisfactory if the free thyroxine index is used as a guideline, the dose of antithyroid is reduced in anticipation of the improvement that usually occurs as pregnancy advances, and surgery is considered whenever the dose of anti-thyroid drug exceeds 400 mg daily during the third trimester.