Caloric requirements for weight gain in subgroups of anorectic patients (anorectic restrictors, anorectic binge-purgers) and weight maintenance in subgroups of anorectic and bulimic patients (bulimics with and without a prior history of anorexia nervosa) were studied in a total of 36 patients. No significant differences were found between subgroups of anorectic patients either in calories to gain weight or to maintain a normal weight. Bulimic patients, as a group, were found to require significantly fewer [corrected] calories than the group of anorectic patients to maintain a normal weight. Bulimic patients with a prior history of anorexia nervosa were found to require more calories for weight maintenance than bulimics with no such prior history. In the entire eating disorder population, there was a significant negative correlation between highest premorbid body mass index (BMI) and calories required to maintain weight. These findings suggest that differences in energy metabolism may be present in the eating disorder subgroups.