The purpose of this study was to determine whether propranolol alone can improve mineral metabolic disorders in thyrotoxicosis. Ten Graves' disease patients and 11 normal age- and sex-matched controls participated in the study. In the untreated Graves' patients, serum levels of calcium (Ca), calcium x phosphorus product (Ca x P), urinary Ca, phosphorus (P), magnesium (Mg), and hydroxyproline (Hp) were higher than in control subjects (P less than .05), intestinal Ca absorption was lower than in control subjects (P less than .05), and Ca, P, and Mg balance were negative (P less than .05). After 40 mg propranolol four times per day (qid) for 28 days, serum triiodothyronine (T3) had decreased (P less than .05), serum reverse triiodothyronine (rT3) increased (P less than .05), serum thyroxine (T4) remained unchanged (P greater than .05), serum Ca and urine Ca and Mg decreased (P less than .05), intestinal Ca absorption increased, Ca balance was corrected, and P and Mg balance was improved (P less than .05). Our results indicate that propranolol can improve the metabolic disorders in addition to the symptomatic manifestations of Graves' disease. The mechanism responsible for the improved mineral balance is unclear, but may be related to beta-adrenergic blockade, increased membrane stability, or a decrease in the thyrotoxic state caused by the therapeutically induced decrease in serum T3.