A review of the psychoneuroimmunological literature is provided with emphasis on studies concerning mental disorders. Initially, research was mainly directed at the influence of life events and stress on immunological functions. More recent studies have focussed on the relationship between mental disorders and immunological functions. The research findings suggest that depression can induce immunosuppression, this effect possibly being age-dependent. However, it is not yet clear whether immunological changes are of clinical relevance. So far the psychoneuroimmunological research concerning schizophrenia has yielded ambigious results.