Biological psychiatry is a technical term that denotes physiological and biochemical approaches to psychiatric aetiology and, despite the usual wider meaning of the word biological, excludes psychosocial approaches. 'Biological' causes of severe psychiatric disorder have been suspected from the earliest times, and in some periods an excessive focus upon them has led to neglect of psychological and social approaches to treatment, to the detriment of patients. It is important that current research into biological psychiatry should be carried forward in conjunction with the important advances that have been made in psychological and social research. The causes of psychiatric illness are complex and it is unlikely that any single approach, biological or psychosocial, will be sufficient on its own. The great potential of biological psychiatry will be realized only if it is viewed within these wider historical and scientific perspectives.