The electroencephalographic changes associated with delirium have been presented in a previous report.1These changes were observed to be reversible to the extent to which the delirium was reversible. The character of the electroencephalographic changes was determined by the intensity, duration and reversibility of action of the noxious factors as modified by the essential premorbid integrity of the central nervous system. In this report further data will be presented to illustrate the reversibility of the electroencephalogram during experimental procedures designed to modify some of the basic physiologic derangements. The effects studied included those of (a) inhalation of oxygen, (b) changes in posture, (c) phases of Cheyne-Stokes respiration. (d) blood transfusion, (e) administration of adrenal cortex substances and (f) infusion of dextrose. MATERIAL AND METHODS Twenty-five patients were studied. Clinical and laboratory observations on these patients, as well as the psychologic and electroencephalographic methods of examination and interpretation, are presented