Following the discovery that the introduction of concentrated solutions of various salts or of dextrose into the blood stream1or the gastro-intestinal tract2of an experimental animal causes a diminution in its cerebrospinal fluid pressure, hypertonic solutions have been administered clinically by different routes in attempts to reduce intracranial hypertension in patients suffering from brain trauma,3brain tumor,4meningitis5or brain edema with acute infections.6However, more recent observations both in animals7and in a small number of human beings8have indicated that the initial decrease in the tension of the cerebrospinal fluid induced by these methods is superseded within from one to three hours by a persistent rise in subarachnoid pressure and an exacerbation of the initial symptoms of intracranial hypertension. The problem, therefore, appeared to require further investigation. It is my purpose in this paper to report a study of