Levodopa-induced dyskinesias frequently limit the clinical efficacy of levodopa therapy in Parkinson's disease. Deanol recently has been reported to be of value in relieving the dyskinesias by acting through a central cholinergic mechanism. Seventeen outpatients with levodopa-induced dyskinesias were given deanol in dosages of 300 to 900 mg per day. The dyskinesias improved in four of the patients, remained unchanged in five, and worsened in eight. In all four patients who showed improvement after institution of deanol therapy, the improvement continued after the patients were switched to a placebo. One of these patients also demonstrated improvement in his parkinsonism, while two others experienced a worsening in their parkinsonism. Deanol does not appear to be effective in the treatment of levodopa-induced dyskinesias.