The entero-hepatic circulation of thyroid hormones is increased in thyrotoxic states. Based on this observation, the use of ionic exchange resins to bind thyroid hormones in the intestine has been tried. The present study evaluates the effectiveness of cholestyramine as an adjunctive therapy in the management of hyperthyroid Graves' disease. Thirty patients with newly diagnosed hyperthyroid Graves' disease were randomly assigned to one of the following treatment groups: methimazole, propranolol and cholestyramine for 4 weeks (group I); methimazole and propranolol for 4 weeks (group II); methimazole, propranolol, and cholestyramine for 2 weeks, followed by 2 weeks of methimazole and propranolol (group III). At the end of the study, total and free T4 as well as T3 levels had decreased more in group I compared with group II: 61%, 78%, 68% in group I compared with 43%, 65%, 50% in group II (P = 0.037 for T4, P = 0.038 for free T4, P = 0.012 for T3). Group III behaved like group I while patients were receiving cholestyramine, but once the drug was discontinued, the rate of decline of thyroid hormones slowed down. We conclude that cholestyramine represents an effective and well-tolerated adjunctive therapy in patients with hyperthyroid Graves' disease, and it produces a more rapid and complete decline in thyroid hormone levels in these patients.