The investigators tested the effect of 120 mg propranolol daily on 21 patients with essential tremor using a double-blind cross-over method and electrical recording of tremor amplitude and frequency. The patients varied in age between 15 and 60 years and had a mean tremor frequency of 10 cps. Propranolol had no effect on the tremor frequency but reduced the amplitude in 15 of the patients. Propranolol was most effective in older patients and in those with slow tremor frequencies.