Dichlorvos was introduced into 42.5 cubic m chambers as an aerosol or in the vapor phase. Aerosols were dispensed by pressurized cans or by a DeVilbiss sprayer using air to atomize the formulation. A specially designed cartridge dispenser and static dispensers were used to introduce the insecticide in the vapor phase. Only the static dispensers gave relatively constant concentrations of the insecticide in the air. Various stored- product insects were exposed to dichlorvos, with emphasis given to bioassays with the adult of the confused flour beetle, Tribolium confusum Jacquelin duVal, the adult of the cigarette beetle, Lasioderma serricorne (F.), and the larva of the black carpet beetle, Attagenus megatoma (F.). Dichlorvos concentrations of 4.0, 2.7, and 1.9 micron g/liter killed 95% of the confused flour beetles after exposures of 4, 8, and 12 hr, respectively. Data on the cigarette beetle and black carpet beetle were not sufficient for establishing statistically the concentration x time relationships. Cigarette beetle mortality exceeded 80% within a limited range of concentrations and exposures. Dichlorvos produced a delayed mortality action for black carpet beetle larvae, as indicated by 26% mortality within 2 weeks after a 24-hr exposure to a dichlorvos concentration of 16 micron g/liter and 87% mortality within 16 weeks after a 24-hr exposure to a dichlorvos concentration of 4.3 micron g/liter.