Five patients with essential tremor were treated with increasing daily doses of propranolol. Tremor intensity was assessed after each propranolol dose had been given daily for a period of at least seven days. The evaluation was made 12 to 15 hours after the last propranolol ingestion. It included a semiquantitative clinical tremor evaluation and quantitative registration with an accelerometer. Electronic integration of the accelerometer curves gave an arbitrary measure of tremor intensity. Plasma propranolol concentration was determined at each tremor measurement. The reduction in tremor correlated with increasing propranolol doses, whereas plasma propranolol concentrations varied widely among individuals and could not be correlated with tremor reduction. Most of the patients had considerable diminution in tremor at low propranolol doses, often with an unmeasurable plasma propranolol concentration. Determination of plasma concentrations has little value in long-term treatment of essential tremor with propranolol. The dosage can be sufficiently guided by clinical evaluation of effect.