Abstract
A simple method of measuring red cell sodium has shown that about 90% of thyrotoxic patients have values above the upper limit of the normal range. Patients taking 0.3 mg of L-thyroxine daily were found to have a significantly higher mean value for red cell sodium than that of the normal controls. It is suggested that patients taking this amount of thyroxine may be hypermetabolic. The determination of red cell sodium may prove useful as a measure of the peripheral action of thyroid hormone.