Propranolol treatment of patients with essential tremor, selected for chronic, nonresting tremor of hands and head causing functional impairment, benefited only one of nine patients during a double-blind study (320 mg per day). No serious cardiorespiratory complications occurred in this screened patient group, but an elderly man became agitated and depressed. We conclude that propranolol does not benefit all patients with essential tremor and that this disorder may be caused by several biochemical mechanisms.