CDP-choline, an intermediate in the phospholipid metabolic pathway supposed to improve the functionality of the dopamine (DA) system, was administered to parkinsonian patients in a double-blind cross-over study versus placebo. All patients were already treated with L-dopa + dopa decarboxylase inhibitor. Clinical evaluations were carried out using the Webster Rating Scale (WRS), the Northwestern University Disability Scale (NUDS) and a semiquantitative rating scale for tremor, rigidity and bradykinesia. CDP-choline treatment showed a significant improvement of rigidity and bradykinesia and a less important amelioration of tremor. NUDS and WRS showed a similar positive result. Comparing the results obtained by placebo, we found that the actual clinical efficacy of CDP-choline regards mainly bradykinesia and rigidity (23 and 33% improvement, respectively). The positive effect of CDP-choline on parkinsonian patients already treated with L-dopa + dopa decarboxylase inhibitor stands for a possible action on the DA receptor through an activation of the phospholipid metabolism.