Explanations of abnormal behavior that emphasize the importance of physiological determinants of disorder are relatively unpopular among psychologists, especially among those who work as clinicians in an ap~ plied setting. The reasons for this are theoretical and historical, as well as practical. Physiology and its associated biological disciplines of bio~ chemistry, pharmacology, and genetics are traditionally more associated with medicine; their use to underpin explanations and treatments of behavioral abnormality has consequently demanded knowledge to which most psychologists are not exposed and skills that are unavailable to them. The dichotomy thus created between medical and psychologi~ cal approaches has caused many psychologists to disregard physiologi~ cal factors. Even when the latter are recognized as important, many psychologists have been unwilling to admit to the fact, in the belief that by doing so they will commit themselves to an overly medical model of psychological disorder, undermining what they see as preferred views of abnormality. As I have become increasingly aware in following the progress of this book, in the United States the theoretical issues in this debate have been further sharpened by professional rivalries (present but less explicit on the European scene from which I write) between medical and nonmedical health care workers, regarding facilities for and approaches to the treatment of the mentally disturbed. Faced with these divisions of interest, psychologists have available two courses of action.