1. Application of the sterile insect technique (SIT) to the facefly, Musca autumnalis DeGeer, is considered. 2. Six-day-old pupae were exposed to ionizing irradiation at doses in the range 100-1600 rads, each treatment being replicated six times. 3. Eclosion was unaffected but fecundity and fertility was inversely proportional to the radiation dose. 4. 1600 rads gave 97% dominant lethality of sperm in treated males and suppressed ovarian development in females. Irradiated flies did not recover fertility. 5. Irradiation of males and females did not affect insemination rates. 6. Sterile males showed a decline in longevity and reduced mating competitiveness. 7. Local eradication of M. autumnalis is considered to be feasible if sufficient diapausing sterile flies are stockpiled and released in early spring, followed by additional releases of non-diapausing flies in late spring and early summer, with further releases of diapausing sterile flies in late summer and autumn.