An electromyographic method was used to study the effect of combination therapy with L-dopa and trihexyphenidyl on tremor in thirty patients suffering from extrapyramidal motor system disease. In this method tremor activity was measured and documented so that the course of the disease could be followed objectively. L-dopa alone was slightly more effective against tremor than was trihexyphenidyl alone. The combination of the two drugs was more effective than either drug used alone, and its side-effects were mild and definitely fewer than had been reported with L-dopa combined with a decarboxylase inhibitor. Good control of tremor with L-dopa and trihexyphenidyl was obtained clinically and verified electromyographically.