The relative efficacy of trihexiphenidyl hydrochloride, amantadine hydrochloride, and low-dose carbidopa-levodopa in reducing parkinsonian tremor was investigated using objective techniques. Trihexiphenidyl and carbidopa-levodopa decreased tremor by greater than 50%. Some patients responded to one drug but not to the other. Amantadine decreased tremor less than 25%. Monotherapy with trihexiphenidyl or carbidopa-levodopa should be the initial treatment for the tremor of Parkinson's disease.