The available data indicate that over half of patients with bulimia nervosa binge and purge daily with repetitions of the binge/purge cycle being common. An understanding of the biobehavioral mechanisms associated with frequent binge/purge cycles may aid the general conceptualization of bulimia nervosa including its development and maintenance. Binging and purging have demonstrable physiological effects that may be partially responsible for the repetition of binge/purge episodes. In the present study, the cephalic phase oversecretion of insulin and high insulin levels subsequent to purging were investigated as possible mediators of repeated binging and purging. Insulin and glucose levels of bulimic and nonbulimic women were measured in response to: thinking about food, the presence of food, while eating, and for the bulimic group, after purging. Bulimic subjects displayed a dramatic reduction in both insulin and glucose after purging the test meal. When these same subjects ate a subsequent meal that was not purged, they displayed elevations in insulin and glucose similar to those of the normal controls. The hypoglycemia resulting from purging appears to be partially responsible for the continuation of repeated binge/purge episodes.