Many animal and plant species are transported across the globe each year. The introduction of an exotic pest species often causes devastating losses in its new country of origin. An unfortunate example of such an exotic insect pest is the soybean aphid, Aphis glycines Matsumura, which was discovered in the Great Lakes region of North America in the summer of 2000. Since its introduction the soybean aphid has rapidly moved across the Midwest spreading to 21 U.S. states and three Canadian provinces as of the 2003 growing season. The soybean aphid has become a serious pest of soybean, causing yield losses in the Midwest of up to 30% and costing farmers millions of dollars annually. Understanding how natural enemies impact aphid populations in the field is an important component in developing comprehensive management plan. The impact of naturally occurring predators in the field on soybean aphid densities and their within-plant distribution was examined using exclusion cages during July-September 2004 and 2005. Plots were surveyed twice weekly for soybean aphid and natural enemy densities. Cage effects on temperature and soybean growth were found to be insignificant. Significant differences in aphid density and aphid location among the soybean plant canopy were found between treatments. These differences between treatments were attributed to the presence of natural enemies which were excluded by caged treatments. Orius insidiosus(Say) was the most commonly occurring predator in the field. The large differences in aphid abundance and aphid location within the plant canopy between years was associated with the higher number of O. insidiosus found in the field in 2005 than in 2004. This study indicates that naturally occurring predators in the field can have a large impact on soybean aphid densities if natural enemies are present at the beginning of the season to suppress aphid population growth.