OBJECTIVE To review the eating disorder research investigating the psychobiological connections between self-starvation and high-level exercising, including both animal experimentation and clinical field studies. In recent years it has been proposed that physical activity plays a central role in the pathogenesis and progression of the eating disorders-in particular, anorexia nervosa. METHODS A review of research from animal experimentation and from clinical field studies investigating the biological and psychological implications of physical activity and starvation in the pathogenesis of eating disorders. RESULTS Animal research indicates that physical activity and starvation seem to potentiate one another and that alterations in the serotonergic system may underlie this process. Similar behavioural results have been found in recent clinical studies with eating-disordered patients, which suggests that physical activity plays a more central role in the development and maintenance of the eating disorders than had previously been thought. CONCLUSIONS The emerging picture is that psychosocial factors seem to provide the most compelling factors in the etiology and onset of the disorder, while biological factors-in most cases induced by severe malnutrition and strenuous overexercising-predominate in the maintenance of the disorder.