Frontal-lobe injuries often adversely affect cognitive functions such as planning and decision making. These are known as executive functions, and they reside largely in the frontal lobes of the brain. In preparation for studies of patients with cognitive deficits, including a large study of Vietnam veterans with frontal-lobe injuries, 3 normal subjects participated in a functional magnetic resonance imaging (fMRI) pilot study of cognitive function while using an interactive virtual apartment constructed with computer-game development software. At least 1 day prior to the fMRI scan, subjects were given a passive tour of multiple environments within a virtual world and then allowed to practice navigating through the world using a joystick and touch pad. Within a week they returned for the fMRI study, in which they were given 2 minutes on each of 5–7 contiguous runs to perform tasks within the virtual apartment that were designed to be increasingly difficult (i.e., task loading). For example, in one of the least difficult runs, they were asked to navigate through a small apartment of 5 rooms and to turn on all of the light switches. In the last and potentially most difficult run, they were asked to find and open all of the closets (4) in the apartment and mentally categorize and count the number of items within the closets. After the data were detrended and filtered, the effects of task performance on brain-activation patterns were computed. There was a statistically significant correlation between subjective rating of task difficulty and pixel intensity in the anterior frontal lobes compatible with highly significant bilateral activation when the more difficult tasks were compared to the less difficult tasks. This study illustrates how virtual environments can be used for more naturalistic studies of executive function, and it provides normative data for later comparison with head-injured patients.