The arterial oxygen saturation in electroshock therapy has been determined with the aid of a photoelectric oximeter. The following observations were made:1. Electroshock causes rather severe, but transitory, hypoxemia.2. Impaired respiration after the convulsion can give rise to severe and rather prolonged hypoxemia.3. If more than one shock is necessary to produce a convulsion the degree of hypoxemia is considerably increased.4. The administration of pure oxygen for a period of ½ to 1 minute (1 minute in elderly individuals) immediately before as well as after the shock considerably reduces the degree of hypoxemia.5. The oxygen administration prolongs the convulsion. The intensity of the convulsion is probably also somewhat increased, thus possibly increasing the risk of skeletal injuries.6. The addition of 6% carbon dioxide to the oxygen gas is a somewhat poorer protection against hypoxia than pure oxygen. Carbon dioxide also appears to increase further the duration of the convulsions.7. When a muscle-relaxing agent is used and oxygen insufflated, a maximum oxygen saturation of the arterial blood can be obtained throughout the treatment. The convulsion is thereby greatly prolonged.Abstract Teaser