Efficiency and safety of amantadine sulfate (AMS) infusions were investigated in late stage complications of Parkinson's disease (PD). In an open-label study, 21 PD patients suffering from motor fluctuations and/or dyskinesias were administered AMS infusions (PK-Merz, 400 mg per day) during seven days. Oral AMS treatment followed. Significant improvement of UPDRS motor scores was observed between day 0 and day 7, remaining improved until day 21. Based on patients' diary notes, both severity and occurrence of hypokinetic "off" state significantly decreased (from 6.6 to 3.1 hours, p < 0.001, average "off" time per day) as well as dopaminergic-induced dyskinesias (from 2.5 to 1.3 hours, p < 0.05, average duration of dyskinesias per day). AMS infusions followed by oral administration appeared as a safe method for improvement of both motor fluctuations and dyskinesias in advanced PD. In advantage to simple oral therapy, AMS infusions allowed fast introduction of a profound and durable treatment effect.