The effect of stress induced by the novelty of a situation was evaluated by means of event-related potentials (ERPs). Potentials, recorded with Fz, Cz and Pz electrodes, were evoked by flashing red and yellow LED diodes. A standard 'odd ball' procedure was used, in which flashes of one color were mentally counted (target stimuli). ERPs evoked by target and non-target stimuli recorded in the first session of the experiment were compared with those recorded at least 40 min later. The early waves and P200 components indicated the increased responsiveness during the initial sessions. Amplitudes of both components were significantly larger. Latencies of the early waves were also significantly shorter. The effects were present in responses to both target and non-target stimuli. In contrast, the latency of P300 wave was significantly elongated during the first recording. Grand-averaged curves indicated also a reduction of P300 amplitude, but when individual waves were analyzed, the effect did not reach the level of statistical significance. It was suggested that the novel situation could be employed as a model of relatively pure stress, useful in the interpretation of other results such as the effects of pain.