ABSTRACT The ‘salt gland’ appears to be the predominant route of sodium and potassium excretion in the marine turtle Chelonia mydas mydas. The kidney of the marine turtle is probably not capable of maintaining a positive water balance in the face of the electrolyte loads presented by sea water and food. Treatment with amphenone reduced the sodium and potassium excretion of fed and saline-loaded marine turtles. The administration of corticosterone partially corrected this reduction. Thus the excretion of electrolytes by the ‘salt gland ‘appears to be, at least partly, dependent upon a fully functional adrenal cortex. The significance of the ingestion of sea water by marine turtles is discussed in relation to the excretion of the large amount of potassium contained in their food.