The ecology of Escherichia coli O157:H7 in cattle is poorly understood. Previously, it has been suggested house flies play a role in dissemination of this pathogen. In this study, eight calves were individually exposed to houseflies that were orally inoculated with a mixture of four strains of nalidixic acid resistant E. coli O157:H7 (Nal^REcO157) for 48 hours. Another eight calves were individually exposed to uninoculated flies and served as the control. Fresh cattle feces (rectal sampling) and drinking water were periodically screened for Nal^REcO157 up to 19 days after the exposure. On day 20, all calves were euthanized and the different parts of the digestive tract were screened for Nal^REcO157. On day 1 after the exposure, all fecal samples and drinking water samples of 5 of 8 calves exposed to inoculated flies tested positive for Nal^REcO157. The concentration of Nal^REcO157 in feces ranged from detectable by enrichment only (< 10²) to up to 1.1 x 10⁶ CFU per gram. Feces of all calves remained positive for Nal^REcO157 up to 13 days after the exposure and the majority (62.5%) of fecal samples were positive until the end of experiment. Contamination of drinking water was more variable and all samples were negative on day 19. Necropsy showed the highest prevalence of Nal^REcO157 in the recto-anal mucosa region, followed by rectal and colonic contents. This data show that house flies can transmit E. coli O157:H7 to cattle and likely play a role in the ecology of this organism in the cattle environment.