Psychosomatic medicine needs a theoretical model for clinical tasks and for research. To start from Freud's psychoanalytic theory (conversion and anxiety neurosis) and Alexander's model of the "vegative neurosis" a system theory concept of the bio-psychosocial model (Lipowski) is presented and discussed critically. Instead of further investigation on the problem of "unity", or on monistic or dualistic views of the mind-body problem, we propose a new theoretical approach. If we focus our interest on nodal points of the bio-psychosocial network we can learn more about somatic-psychosocial interaction and can develop practical consequences for research and clinical issues.