We studied the acute and chronic effects of propranolol and primidone in essential tremor by administering long-acting propranolol (80 to 160 mg/d) and primidone (50 to 250 mg/d) to 50 patients. We evaluated patients at 1, 3, 6, 9, and 12 months after treatment and assessed tremor by subjective rating by patients, clinical scoring, and tremorgraphic (accelerometer) recordings. Acute adverse reactions occurred in 8% with propranolol and 32% with primidone. Propranolol was without therapeutic effect in 30%, and 32% had no benefit from primidone. Significant chronic side effects occurred in 17% taking propranolol and in 0% with primidone. Tolerance to drug effect occurred with chronic treatment in 12.5% of patients with propranolol and 13.0% with primidone. We conclude that propranolol and primidone are effective long-term treatment for some patients with essential tremor. Acute adverse reactions with primidone and side effects with chronic use of propranolol hamper therapy.