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Retrieval of information from episodic memory involves the processes invoked by the attempt to remember (retrieval attempt) as well as processes associated with the successful retrieval of stored information (ecphory). Previous PET studies of memory have shown an activation of the prefrontal cortex in memory retrieval tasks, and we hypothesised that this activation represents retreival attempt, not ecphory. This hypothesis was directly directed using [15O]H2 PET imaging in 19 healthy subjects who performed three matched tasks which involved different levels of retrieval attempt and ecphory. The results showed that retrieval attempt was associated with activation of the prefrontal cortex, right greater than left, while ecphory involved the posterior cortical regions. These findings illuminate the functional role of the different neuroanatomical regions involved in episodic remembering.