Experimental and clinical study of mexidol efficacy in the complex therapy of Parkinson's disease has been carried out. It is shown that in a Parkinsonian animal model using oxotremorine, mexidol reduces Parkinsonian symptoms and decreases expression of neurophysiological changes caused by oxotremorine. Neurohistological study of substantia nigra neurons in a Parkinsonian model using MPTP revealed a neuroprotective effect of mexidol. An assignment of mexidol (4,0 ml intravenous in drops during 10 days) to patients with Parkinson's disease, receiving the basic therapy with antiparkinsonic drugs, reduced tremor, rigidity and bradykinesia. The most marked effect was observed in patients with prevalence of trembling symptoms at early stages of the disease. The results of clinical study have been confirmed by electromyographic and electroneuromyographic data.