The risk of minor cognitive decline and dementia increases with advancing age. Thus, as the average lifespan of humans continues to rise the number of people that are affected by dementia will rapidly increase. Dementia is described as multiple cognitive deficits that adversely impact activities of daily living. Lifestyle behaviors may prove critical in delaying or preventing the onset of cognitive decline and dementia. Specifically, exercise has been shown to decrease reaction time, improve executive function, and maintain performance on gross measures of cognitive ability in an aging population. Further, physical activity becomes even more important when the genetic susceptibility for dementia rises. Apolipoprotein (APOE) e4 is one such risk factor and is associated with the development of Alzheimer's disease (AD). Severe memory loss is one defining symptom of AD and greatly reduces quality of life for afflicted individuals. The purpose of this investigation is to determine the specific behavioral impact of physical activity on those who are genetically at risk for AD compared to those who are not. Sixty cognitively normal individuals between 50 - 70 years old were assessed on medical history, gross cognitive function, physical activity, memory performance (Sternberg memory task), executive control function (Eriksen flanker task), and finally APOE genotype. Using hierarchical regression techniques, memory and executive function scores were regressed on age, education, genotype, physical activity, and the interaction between genotype and physical activity. Analysis revealed that on the more difficult conditions of the memory task as physical activity level increased, reaction time significantly decreased for APOE e4 carriers. No such relationship existed for noncarriers. These results imply, compared with other cognitive challenges, physical activity serves a protective role for maintaining memory, particularly in those who are at a genetic risk for developing dementia.