Amantadine is generally used in the prophylaxis of infection with influenza A, in the treatment of Parkinson's disease and in the treatment of neuroleptic side effects. In this study acute effects of amantadine infusions on event-related potentials (ERP) were studied in 20 mildly demented patients diagnosed according to DSM-III-R criteria. Each patient was treated, in randomized order, with 0.2 g amantadinesulfate in 500 ml NaCl and 500 ml NaCl placebo, i.v. over one hour with an interval of two weeks inbetween. ERPs were investigated in an auditory odd-ball paradigm before as well as 5 hours after the infusion. In addition to 17 EEG records, vertical and horizontal EOGs were recorded. After EOG-minimization and visual artifact rejection the peak latencies of the spatial average were determined by an automatic procedure. There was no effect of amantadine on ERP latencies. N 1 of the non-target showed a trend towards amplitude augmentation, P2 amplitude was reduced. As compared to placebo, P300 amplitude of targets was significantly augmented by 3.1 V (30% of pre-treatment value), confirming the hypothesis that amantadine may influence the P300 amplitude in the sense of an improved availability of cognitive processing resources.