The mechanism of aspirin analgesia is still unclear, but it is generally assumed that aspirin exerts its analgesic effect mainly on peripheral nociceptors. In this study, we demonstrate possible brain effects of 975 mg aspirin in man. When brain electrical potentials evoked by painful electrical tooth shocks were examined, aspirin was observed to significantly reduce the amplitude of the late waveform components, but it did not affect the earlier components. Since our earlier findings suggest that early waveform components reflect the energy transmission and the late components manifest the brain activities in an individual's perception of painful information, we postulate that aspirin may act centrally in pain processing.