Grain odour influenced oviposition behavior was investigated amongst free-flying, gravid Ephestia cautella females. Females released into a 5m3 or 10m3 cage readily located, and oviposited in the vicinity of small sources of diffusing grain odour or grain odour in an airstream. Oviposition increased at the odour sources when 30per thousand of an airstream carrying grain odour was replaced by CO2, whereas it decreased when 95per thousand was replaced by N2, and did not change when 60per thousand was replaced by either CO2 or N2. Females relased in to a wild-runnel responded to grain odour by increased frequency of upwind flight and by landing at the odour source. These responses are discussed in the context of grain stores sealed for treatment with controlled atmospheres of fumigants.