Eighty-five patients with an established diagnosis of primary Parkinson's disease were randomly assigned to receive their usual dose of levodopa (mean, 381 mg daily) plus 1,200 mg of citicoline daily or half their usual dose of levodopa (mean, 196 mg daily) plus the citicoline. Results of the Webster Rating Scale, a pegboard test, drawing, writing, and walking tests, a test of emotional state, and an overall assessment, administered before and after four weeks of treatment, revealed no significant between-group differences. Improvements on the tests were shown by more patients who received half their levodopa dose plus citicoline than by those who continued to receive their usual levodopa dose plus the citicoline. It is concluded that the levodopa-saving effect of citicoline could be used to decrease the incidence of side effects and retard the loss of efficacy of levodopa in long-term treatment.