Cestodosis in battery-housed laying hens severely reduced egg production particularly at the time of peak production. Hens were able to consume large numbers of Musca domestica, the intermediate host of Choanotaenia infundibulum following the use of an aerosol insecticide to control flies. A considerable discharge of cestodes followed the use of "Lintex" in the feed resulting in a marked improvement in egg production. The use of an insect growth regulator in the feed showed promise in controlling the breeding of flies.