Prednisone (Meticorten) was introduced in November, 1954, as an effective antirheumatic medication.1In animals, it was found to produce involution of the thymus, eosinopenia, and glycogen deposition in the liver, as do cortisone and hydrocortisone. The similarity to cortisone in its molecular structure2and biological effects led us to compare the two compounds and attempt to assess the possibility of prednisone supplanting cortisone. The work was done in human subjects with rheumatoid arthritis, systemic lupus erythematosus, pemphigus, periarteritis nodosa, and diabetes mellitus associated with the nephrotic syndrome. One additional study was carried out in animals by the Selye granuloma pouch technique.3 SODIUM, POTASSIUM, WATER, AND GLUCOSE METABOLISM Two patients with well-documented sustained rheumatoid arthritis of more than five years' duration were admitted to the metabolism ward of the Presbyterian Hospital, New York. Both patients were placed on a constant diet and given prednisone, 30 mg. in 24