Abstract
A rapid, easily performed in vitro test of thyroid function was evaluated in the sera of 238 subjects. The charcoal liothyronine (T3) I 125 ratio was decreased in thyrotoxicosis and increased in myxedema. Abnormalities in the plasma protein binding of thyroid hormone were reflected in abnormal ratios. The prior administration of iodine-containing compounds did not result in abnormal tests.