The effect of surgical operations on the urinary excretion of iodine, corticosteroids, uric acid, and ketosteroids was examined in 11 subjects. The majority showed a marked rise in the excretion of iodine which occurred within the first 24 hr. after operation; thereafter iodine excretion tended to decline, being back to normal levels by the third postoperative day. Over the same period of time the excretion of corticosteroids increased and was still elevated on the third postoperative day. The excretion of uric acid was elevated in some but not all of the subjects while no consistent trend in any direction was noted as regards the excretion of ketosteroids. The level of inorganic plasma iodine was elevated one to two hours postoperatively, while the level of protein bound plasma iodine was unchanged. No conclusion was reached concerning either the source of the extra iodine or the relationship between the increased excretion of iodine and the increased excretion of corticosteroids.