Larvae of the blueberry maggot (Rhagoletis mendax Curran) were raised on apples (Malus domestics Borkh. cv. Idared), and exposed larvae were treated 48 hours with CO concentrations ranging from 0% to 100% at O concentrations of 2%, 5%, or 20% (0% for the 100% CO) at 5 or 21C. Blueberry maggot survival was reduced to 10% when the larvae were subjected to CO concentrations > 45% at 21C. Fumigation was more effective at 21C than at 5C. Oxygen at 2% or 5% did not reduce larval survival when compared with treatments containing 20% O. In a separate experiment, six commercial shipments, each consisting of four hundred eighty 0.5-liter containers of infested lowbush blueberries (Vaccinium angustlfolium Ait.), were placed in a large fiberglass tank and fumigated with 54% CO at 21C. The blueberries were sampled for quality and larval survival after 24 and 48 hours of CO treatment. Atter 48 hours, 9% of the blueberry maggots in infested blueberries survived fumigation with 54% CO, while 68% of maggots survived in air. The quality of fumigated lowbush blueberries was not adversely affected by fumigation with 54% CO for up to 48 hours, as indicated by marketable berries, berry weight, split berries, shriveled berries, epicuticular wax (bloom), firmness, soluble solids and titratable acid concentrations, offflavors, and skin browning.