‘Biological factors’ explores research into the cause of schizophrenia. Some have sought a biological basis for the disorder, while others have looked for social or psychological causes. In recent years, however, the emphasis has been upon biological causes. Twin and adoption studies provide good evidence that genetic factors play a major role in the development of schizophrenia, but it is clear that this role is not absolute. Several genes may interact with one another and with environmental factors to influence susceptibility to schizophrenia. Neuropathological and neuro-imaging studies have sought a relationship between the symptoms or course of the illness and structural brain changes, but consistent findings have not been shown.