Soybean oil (SO) is considered an active ingredient in commercial BiteBlocker™ insect-repellent products. Our objective was to test mechanisms by which SO exhibits repellency, using the yellow fever mosquito, Aedes aegypti (L.) (Diptera: Culicidae), as a representative blood-feeding insect. In dual-port glass-cage olfactometers, human hands treated with SO at various concentrations attracted as many mosquitoes as did untreated hands, indicating that SO has no long-range repellent effect. In contrast, hands treated with N, N-diethyl-3-methylbenzamide (DEET) attracted significantly fewer mosquitoes than did untreated control hands. In cage experiments, treating an area of a human forearm exposed to A. aegypti with SO provided no protection against bites, whereas treating it with DEET did. These results indicate that SO has no short-range or contact repellent properties. Both DEET and the BiteBlocker™ product conferred protection for periods similar to those previously reported. Based on our data, classification of SO as an active mosquito repellent should be reconsidered.