Forty-eight sequential narcoleptic patients were treated with propranolol (80-240 mg/day) for an average period of 18.4 months. Initially all patients received single drug therapy; after 10 days or longer, however, 50% of patients also received tricyclics or stimulants because propranolol alone did not sufficiently suppress the narcoleptic symptoms. Fifty percent of patients judged the initial effectiveness of propranolol on daytime sleepiness to be good to very good; in these patients the effects seemed comparable to that of pemoline. Within 6 months, however, the effectiveness started to decrease, and after 26 months only 8% (2 out of 24) of those patients taking the single drug were satisfied with propranolol therapy alone. Side effects included disturbed night sleep, decreased blood pressure, increased lethargy, allergic skin rash, and asthma; 58% of the patients dropped out of the study after 26 months. Vigilance tests during the first 4 months (16 patients) showed significant improvements in all test criteria, including a shorter reaction time. All-night polygraphic electroencephalogram recordings of 14 patients on the eighth and ninth day of medication showed that average total sleep time decreased by 5.7%, but other sleep characteristics did not change significantly.