Heart rate and vagal tone were assessed during sleep and bed rest conditions in nine patients with bulimia nervosa (BN), six patients with concomitant anorexia nervosa and bulimia nervosa (AN + BN) and five control subjects. During bed rest conditions AN + BN patients had significantly lower heart rates than BN or control subjects. During sleep, the heart rate differed significantly for all three groups. The AN + BN group had a significantly lower heart rate than either the BN or control groups and the BN group had a significantly lower heart rate than controls. On the other hand, measures of vagal tone, based on respiratory sinus arrhythmia, were significantly elevated in both patient groups compared to controls. These findings suggest that the bradycardia during sleep in BN patients may be primarily due to hypervagal activity, but the greater bradycardia demonstrated in those patients with both AN and BN may result from hypervagal activity coupled with reduced sympathetic activity.