Deanol appears to be a safe and effective drug for the treatment of levodopa-induced dyskinesias in patients with Parkinson's disease. Of 11 such patients treated with deanol in a single-blind controlled study, dyskinesias were completely eliminated in eight patients and were greatly improved in a ninth. One patient did not respond to the treatment. The remaining patient discontinued the medication after two days because of a feeling of fatigue. Otherwise no side effects were noted and no laboratory abnormalities were encountered. Improvement began 10 to 14 days after initiation of treatment. In five patients treated successfully with deanol, placebo was substituted after four weeks, and dyskinesias reappeared within three to eight days.