The effect of cinnarizine on motor function in Parkinson's disease was evaluated in a randomised double-blind parallel study of 20 patients. Both groups were comparable in age, duration of the disease, dose of levodopa and degree of disability. A significant worsening of mobility was observed in patients treated with cinnarizine (75 mg bd), whilst no change was recorded in patients receiving placebo. Cinnarizine should be added to the list of drugs capable of aggravating Parkinson's disease.