28 patients with Parkinson's disease and long-term levodopa therapy have received additional selegiline (10 mg/d) over the past 3 years and been followed up for a mean period of 18.8 months. Two thirds improved with a reduction of global disability and amelioration of end-of-dose effects, nocturnal and early-morning akinesia. Peak-dose dyskinesias tended to increase with selegiline while biphase and off-period involuntary movements improved in some cases. Patients already on maximally tolerated doses of levodopa and those with severe on-off swings did not gain significant benefit. 8 of 18 responders lost their initial response within 1.5 years.