The Federal Republic of Germany has eight specialist behavioural therapy hospitals which have altogether 1,400 beds. The possibilities and limits of in-patient treatment will be elucidated using the example of the Specialist Psychosomatic Hospital in Bad Pyrmont. A biosocial understanding of illness serves as the theoretical and ideological basis as well as a means of communication for all health workers. We understand Behavioural Therapy/Medicine as being the clinical application of knowledge and techniques derived from the experimental analysis of human behaviour (e.g. learned behaviour theory). This knowledge and these techniques are applied to the diagnosis and treatment of mental or psychosomatic illnesses or disorders. It is important to investigate the functional relationship between the courses of their in-patient psychotherapy, our patients are made into,,experts'' for their own problems (through guidance in self-observation, diary-recording, recognition of own coping strategies etc.). A functional systems-model of his illness must be made available to the patient in simple and lay terms so that he may himself understand it clearly. By,,motivation work'', we understand that the patient should be actively encouraged to use all his potential and skills to get to grips with his psychological and social problems. Our motto is,,act, donxt be acted upon''. The total treatment programme should remain clear to the patient in each phase. He is motivated by us to responsible activites of his own. Psychotherapy doesnxt take place primarily in the consulting room, it is rather the way in which the patient puts experiences newly-won during individual and group psychotherapy into action which is decisive for the further course of the treatment (Behaviour testing and practice). Organisational Aspects: Thirty doctors and psychologists are responsible for 180 patients. Twenty nurses are specially trained in the diagnosis and modification of behavioural problems. Adjacent to individual psychotherapy we differentiate between three forms of behavioural group therapy: 1. Problem-solving groups; 2. So-called standard groups (muscle relaxation and assertiveness training) and 3. Groups with special indications such as e.g. behavioural therapy of pain, depression, eating disorders etc. Ten people work in the so-called rehabilitational/educational department. This consists of social therapy, occupational therapy, sport and movement therapy, physiotherapy and remedial gymnastics. The psychopathological and behavioural medical data of all patients are recorded by computer to form a basic documentation which may later be used for retrospective investigations.