Nitrogen (N) loss from cattle dung was measured in dishes of fresh feces exposed outdoors in a screened cage.Musca domesticalarvae were used to determine the contribution of coprophagous Diptera to this loss. Little N was lost from naturally dried pads when insects were absent. Nitrogen loss from artificial 960-g dung pads exposed to other insects in the field did not exceed 13.5% after 16 days. Ten days after infestation of a series of dung pads with different numbers of fly larvae, the total N content of the dung was found to have decreased with each increase in the degree of fly infestation. Heavy infestations of dipterous larvae caused the loss of more N than was incorporated into insect tissue.