Working memory is the ability to maintain and manipulate information over short intervals. One task frequently used to investigate working memory is the delayed-response task (and its variants). In this task, each trial begins with the presentation of an initial stimulus (S1), followed by an unfilled delay interval, and ends with a second stimulus (S2) which prompts a response requiring the subject to reveal whether or not the critical information regarding S1 was maintained across the delay interval. The delayed-response task reliably activates a fronto-parietal circuit comprised of dorsolateral prefrontal cortex (PFC) and the intraparietal sulcus (IPS). Although numerous recent studies have attributed activation during execution of this task to working memory maintenance demands, the delayed-response task has many nonmnemonic response-related components that may activate these regions. Using functional MRI (fMRI), we examined activity profiles within frontal, parietal, and other regions of interest while subjects performed delayed-response tasks in which mnemonic demands were minimized and response demands were manipulated (e.g., response planning, preparation, and execution). We argue based on the results of 4 experiments that the "work" in working memory consists of both mnemonic and response functions that have dissociable neuroanatomic foci within prefrontal and parietal cortices.