The relative and seasonal abundances of naturally occurring pupal parasitoids of flies on dairies in New York and Maryland were determined. Of the 10 parasitoid species found, Muscidifurax raptor Girault & Sanders was the most abundant parasitoid collected. Most of the parasitization by the 3 predominant parasitoid species occurred in August, September, and October. Total parasitization was fairly evenly distributed over all types of fly-breeding microhabitats, but M. raptor was the only parasitoid species found to be abundant in a variety of both indoor and outdoor fly-breeding microhabitats. A statewide assessment of the frequency of fly resistance to commonly used insecticides suggested that the future usefulness of all currently registered insecticides is extremely limited. The effectiveness of an integrated pest management (IPM) program for flies that included M. raptor releases, frequent manure removal, and occasional use of pyrethrin space sprays was evaluated. Fly populations on dairies following the IPM program were approximately ½ those on the conventional farms, and fly reduction was achieved with 80% fewer insecticide treatments. The program was developed from a solid research base and relies on mass-reared parasitoids, a rigorous manure management–sanitation program, and the judicious use of insecticides. In the long run, such an IPM program will reduce farm expenditures, lower insecticide inputs, reduce or delay insecticide resistance and, very importantly, help keep peace with neighbors.