The mortality of female Aedes aegypti exposed to an ultralow-volume (ULV) aerosol for 15 min and then transferred to clean cages was compared to the mortality of females exposed to the contaminated sentinel exposure cages. ULV aerosol sprays of fenitrothion (50% AI) were dispersed at 180 and 205 ml/min, and ULV aerosol sprays of bendiocarb (18.87% AI) were dispersed at 90 and 120 ml/min in an open field. At 24 h after exposure, the mean percentage of mortality of Ae. aegypti in cages previously exposed to insecticides was 87% at 46 m and 71.8% at 91 m downwind of aerosol generation for the four flow rates. The mean percentage of mortality of Ae. aegypti exposed to the aerosol and then transferred to clean cages was 74.5% at 46 m and 68% at 91 m. Insecticide droplets deposited on exposed cages caused significant mortality to Ae. aegypti. Data show that sentinel mosquitoes used in insecticide bioassays should be transferred into clean holding containers as soon as possible after exposure to prevent biasing of results from insect contact with insecticide deposited on cage walls and screens.