This paper reflects on the place of psychoanalytical thinking in a scientific context in which mental illness is increasingly being reduced to physiological and chemical factors. A small series of neurological patients with severe emotional disturbances is presented, in order to demonstrate that emotional symptoms can be neither described nor explained in physical terms. Even in cases where an organic aetiology is indisputable, physiological factors can only be invoked to explain somatic symptoms and the physiological correlates of mental symptoms. The mental symptoms themselves can only be understood psychologically.