Soybean aphid, Aphis glycines Matsumura, poses a serious threat to soybean, Glycines max L., production in the United States and Canada. High soybean aphid densities damage soybean plants by reducing plant height, pod number, and yield. Since its introduction, foliar insecticides have been the only method for control. Seed treatments may provide producers with an alternative to foliar sprays because delivery in this fashion should cause less harm to beneficial insects. Our objective was to evaluate the efficacy of Cruiser in suppressing soybean aphid populations. In 2003 and 2004, we conducted a lab bioassay using excised leaves collected from field plots to assess mortality under controlled conditions. Soybean aphid populations in the field were counted weekly in replicated field plots in multiple locations. Cumulative aphid days, total yield, and yield component analysis were calculated. In the laboratory bioassay, Cruiser caused 50-65% mortality of soybean aphids within 24 h while 70-80% mortality was observed after 48 h. Percent mortality caused by Cruiser declined within 2 wk after soybean emergence and no significant soybean aphid mortality was observed by 4 wk post emergence. In 2003, the 50 g rate of Cruiser significantly reduced the cumulative aphid days by 40% in both field locations. Though the 30 g rate caused mortality in the lab, it did not significantly reduce cumulative aphid days and yield was unaffected While yield with the 50 g rate was increased by as much as 42% compared to the untreated control.