[en] Objective: To study the clinical significance of the determination of plasma β-EP levels with RIA in patients with Parkinson's disease (PD). Methods: The plasma levels of β-EP were determined with RIA in 35 patients with PD and 30 controls. Results: The plasma levels of β-EP in patients with PD were significantly lower than those in controls. The levels were decreased more significantly in those patients who were elderly, severe, demential and depressive. Conclusion: The decreased plasma levels of β-EP in PD patients might play some role in pathogenesis and were closely related to the severity of the disease and prognosis. (authors)