The aim of this study was to assess the effects of high-dose (i.e. 1000 mg per day) intravenous methylprednisolone (HDMP) on event-related potentials (ERPs), elicited by a standard auditory 'oddball' paradigm, in patients with clinically active multiple sclerosis. In a double-blind study design, forty-four consecutive inpatients were randomly assigned in two clinically similar groups of 22 subjects each; one treated with HDMP for five days, and other with placebo. ERPs were recorded before and after the treatment. After HDMP therapy the P3 peak latency was significantly shortened (P=0.006), while peak latencies of other waves (i.e. N1, P2, and N2) remained unchanged. On the other hand, ERPs were uninfluenced by placebo treatment. Our results suggest the beneficial effect of intravenous HDMP therapy on, at least some aspects of, cognitive processing capabilities (as assessed by the auditory ERPs) in patients with multiple sclerosis.