Selegiline HCl (MAO-B(R)) is a levorotatory acetylenic derivative of phenethylamine. The drug is an enzyme-activated irreversible inhibitor of monoamine oxidase (MAO), also known as mechanism-based, kcat, or "suicide" inhibitor. We carried out an open, non-comparative clinical study prospectively to investigate whether the disability of patients with Parkinson's disease could be improved during the first 3 months by Selegiline (MAO-B : 5-10 mg/day). Selegiline (MAO-B ) has been administered as monotherapy or combination with levodopa. A clinical trial was conducted over 3 months with 23 patients in our hospital. Sym- ptomatology was assessed on Unified Parkinson's Disease Rating Scale (UPDRS). Results obtained to data, indicate that UPDRS score was significantly improved at the end of 3 months. Adverse effects were rare and minor. Therefore, this study confirmed that Selegiline (MAO-B ) has proved itself to be a safe and effective monotherapy or adjuvant in long-term levodopa therapy of Parkinson's disease.