The effect of doses of propranolol hydrochloride, 80 to 800 mg/day, was investigated in 15 patients with essential tremor. The dose was increased by 80 mg weekly. Tremor was recorded by an accelerometer and its amplitude and frequency was determined by spectral analysis. Serum propranolol level was measured by radioreceptor assay. Tremor control varied greatly from complete suppression at 80 mg/day to no reduction at 800 mg/day. Mean serum propranolol levels increased with increasing dosage, but they did not correlate with tremor suppression. Five patients did not tolerate doses higher than 640 mg/day. Maximum tremor suppression occurred within a dose range between 160 and 320 mg/day. Higher doses did not cause additional tremor reduction.