To the editor: We read with interest the recent report of Kales and colleagues (1) of use of propranolol in four patients with narcolepsy. We recently documented beta-adrenergic hyperresponsiveness in patients with narcolepsy and related conditions of impaired wakefulness (2) by observation of abnormal, excessive increases in heart rate during intravenous infusion of isoproterenol, a procedure that frequently provoked panic attacks in such patients but not in control subjects. Other data similarly suggested increased adrenergic tone in these subjects, and their autonomic instability seemed analogous to a behavioral tendency to swing between extremes of lethargy and anxious, almost hyperactive behavior.