Event-related brain potentials (ERPs) were recorded during an incidental learning paradigm. Recall and recognition were better for words initially presented in tasks requiring semantic decisions (i.e., 'is it living?' or 'is it edible?') than for words in tasks requiring non-semantic decisions. ERPs elicited during performance of these tasks were predictive of subsequent memory performance. A late positive ERP elicited by words later recalled or recognized was larger than that elicited by words later forgotten. This enhanced positivity for to-be-remembered words could be accounted for, in part, by the fact that words in semantic tasks were remembered better and elicited larger ERPs than did words in non-semantic tasks. Similarly, words followed by affirmative rather than negative decisions were associated both with better recognition and with larger ERPs. However, ERPs were sensitive to processes that influenced later memory performance even within an individual semantic task and within the affirmative decision condition. In addition, results showed that the ERP differences based on later memory performance did not necessarily arise from amplitude variation in P3 waves that occurred at the same time.