Psychotic systems are end-products whose structure can be understood only by examining their origins in the prepsychotic phase and nonpsychotic layer. The psychotic part of the personality has lost contact with reality, but the therapist can secure 'a foothold on nonpsychotic territory' and thereby increase ego strength. The ego is thus enabled to surmount previously powerful dangers, and released energies can now remain at the disposal of the healthy part of the personality. The relationships and differences between psychotic and nonpsychotic defenses are discussed. As to the causes of schizophrenia, Katan suggests that not only constitutional and psychogenic but also endocrine factors must be considered.