Event-related potentials (ERPs) evoked by light flashes and auditory tones in a standard odd-ball procedure were recorded from Fz, Cz and Pz scalp sites. Tonic pain was evoked by immersion of the hand in cold water (5 degrees C). Significant effects of pain were found in responses to target stimuli but not in responses to non-target stimuli. P300 wave was affected more than the earlier P200 component. The reduction of P300 amplitude was the strongest effect, both in auditory and visual tests. P300 latency was not significantly affected. Difference curves (target minus non-target ERPs) showed the additional effects: latency of P200 component was elongated and its amplitude enlarged but only in auditory experiments. In control experiments with warm water stimulation no significant alterations of P300 or P200 components were found. The results show that the effect of tonic pain is specific: it predominantly affects the processes that manifest themselves as amplitude changes of P300 components in responses to target stimuli.