Event-related potentials (ERPs) were recorded while subjects performed two different source memory retrieval tasks. Each task was preceded by a study phase in which subjects heard an equal number of words spoken in a male or a female voice. A cue preceding each word indicated whether the subjects should make an active/passive (action) or a pleasant/unpleasant (liking) judgment to the word. In one retrieval task (the voice condition), subjects made a three-way distinction between new (unstudied) words, and words that had been spoken by the male or the female voice at study. In the second retrieval task (the task condition), subjects distinguished between new words, and words to which they had made an action or a liking judgment. All test words were presented visually. In keeping with previous findings, the differences between the ERPs to correct memory judgments for old and new items were characterised by two temporally and topographically dissociable modulations, with right-frontal and left-parietal maxima respectively. These 'old/new effects' displayed different sensitivities to successful retrieval of either voice or task information, providing further evidence that they index functionally dissociable processes. The direct comparison of the ERPs to correct rejections in the voice and task retrieval conditions revealed reliable differences over frontal scalp, suggesting that, irrespective of whether retrieval is successful, neural processing differs according to the source retrieval demands of the task.