The available knowledge about the pathogenesis of multifactorial ("endogenic") mental diseases is insufficient. The currently employed prophylaxis may, therefore, be characterized as only an initial stage of the development of research programmes. A programme on the identification and study of the constitutional and genetic carrier should be coupled with a programme on the investigation of psychosocial factors which serve as triggers for a hereditarily liable individual. The main and most difficult task associated with it is the determination of the so far evading specificity of interaction of biological factors with those social factors in these individuals which remain nonpathogenic for most people. With regard to secondary prophylaxis of particular importance nowadays becomes the early detection and diagnosis of psychic disturbances at the borderline level, predominantly under general in- and outpatient conditions.