The tremorolytic effects of primidone and phenobarbital in essential tremor of hands and head were compared in a double-blind, placebo-controlled trial. Quantitative measurements of tremor were obtained in 15 patients by means of an accelerometric method. Only primidone proved to be superior to placebo in reducing hand tremor, suggesting that its tremorolytic effectiveness is largely dependent on the parent drug rather than its metabolite phenobarbital. Head tremor tended to improve only in three out of six patients with both primidone and phenobarbital, but, likely due to the small number of affected patients, the effect failed to reach statistical significance.