In a study of shock from hemorrhage using a large number of dogs, it was observed that one dog recovering from anesthesia with pentobarbital Na returned to anesthetized state upon intraven. injn. of glucose. Similar results were obtained sporadically with several other dogs. It was later found that a small percentage of normal dogs given pentobarbital Na reacted to subsequent intraven. injn. on awakening as did the shocked dogs. Similar results were obtained also with guinea pigs, rabbits, hamsters, with some modification in the reactions. Discussion of the mechanism of the reaction is offered. It appears there is a potentiating effect of barbiturate anesthesia by glucose and its metabolic degradation products and that the return to anesthesia after waking from barbiturate sleep is probably due to a potentiating effect of these substances on the subanesthetic level of barbiturate in the blood.