Event related potentials to visually displayed pseudowords were registered from thirteen subjects. In a differential conditioning paradigm half of the pseudowords had previously been paired with a painful electric shock ("shock words"), the other half had been presented without shock ("non-shock words"). Subjects' task was to decide if the words had been presented during the conditioning phase or not. Larger N100 amplitudes and a more negative-going slow wave 400-800 msec after word presentation were found for shock as compared to non-shock words. This effect was stronger over the left as compared to the right hemisphere. We suggested that this left-lateralized negativity might reflect the activation of a cell assembly representing the memory of the learned word-shock contingency. Furthermore, the increased N100 amplitude elicited by shock as compared to non-shock words may be interpreted as an increased attentive facilitation for aversive pain-related information as a consequence of conditioning.