The subject is approached from three points of view. (1) The arguments for and against a death instinct. (2) The limits of the pleasurepain principle. (3) The definition of sadism and masochism. The energy, which expresses itself in those phenomena which led Freud to postulate the death instinct, should be called destrudo. Destrudo, though it may work destructively, is necessary to the preservation of life, its function being to make the organism aware of danger.