Previous work in nonhuman primates and in patients with frontal lobe damage has suggested that the frontal cortex plays a critical rolein the performance of both spatial and nonspatial working memory tasks. The present study used positron emission tomography with magnetic resonance imaging to demonstrate the existence, within the human brain, of two functionally distinct subdivisions of the lateral frontal cortex, which may subserve different aspects of spatial working memory. Five spatial memory tasks were used, which varied in terms of the extent to which they required different executive processes. When the task required the organization and execution of a sequence of spatial moves retained in working memory, significant changes in blood flow were observed in ventrolateral frontal cortex (area 41) bilaterally. By contrast, when the task required active monitoring and manipulation of spatial information within working memory, additional activation foci were observed in mid-dorsolateral frontal cortex (areas 46 and 9). These findings support a two-stage model of spatial working memory processing within the lateral frontal cortex.