Résumé : The effect of dextrothyroxine on blood-lipids has been compared in two groups of euthyroid, hypercholesterolæmic women, ten with evidence of asymptomatic autoimmune thyroiditis and twenty-four controls. Dextrothyroxine 2 mg. per day for a month followed by 4 mg. per day for a month lowered serum-cholesterol levels in both groups, but after the second month the thyroiditis group had significantly lower (and near normal) cholesterol levels compared with controls. Since patients with asymptomatic thyroiditis are at risk of coronary heart-disease, it is suggested that a prospective trial of thyroxine-replacement therapy is warranted. © 1971.