Daily measurement of mood, and the occurrence of specific eating behaviours, were assessed concurrently over an eight-week period in a sample of 50 patients meeting diagnostic criteria for bulimia nervosa. Results of observer-rated scales of mood showed a significant reduction of scores, whereas self-assessment of mood showed no change over the study period. Negative mood states, although not severe, were more marked when the specific behavioural symptoms of binge-eating, vomiting, or purging occurred, and they increased as abnormal eating behaviours accumulated. It is suggested that the accompanying dysphoric mood states of bulimia nervosa are likely to be a secondary manifestation related to the presence of abnormal eating symptoms, and that they do no constitute a primary depressive illness.