Technical Abstract: The MRU methods have been used to study the prevalence of Escherichia coli O157:H7 in cattle carcass, hide, and fecal samples. Sensitivity of these methods for recovery of injured cells has now been determined. Ninety-one percent of the pre-evisceration carcass samples tested positive for E. coli O157:H7 when inoculated with five to ten CFU. For hide samples, 100% tested positive for E. coli O157:H7 when inoculated with 30 to 50 CFU. At lower inoculum levels, substituting a commercially available wash buffer for phosphate buffered saline (PBS)-Tween 20 wash buffer during immunomagnetic separation improved recovery of the target organism. When comparing naturally contaminated samples, substituting a PBS-CHAPS buffer for PBS-Tween 20 also had a positive effect on recovery of E. coli O157:H7 from hide samples. The standard MRU method identified 96% of the fecal samples as positive when inoculated with 300 to 400 CFU (per 10 g). The addition of a phosphate buffer to the tryptic soy broth enrichment improved recovery of E. coli O157:H7 from feces. Using the modified enrichment, 92% of the samples were identified as positive when inoculated with 10 to 30 CFU (per 10 g). When naturally contaminated fecal samples were split and analyzed, 26% tested positive for E. coli O157:H7 by the MRU method and 39% tested positive using the modified enrichment. Data presented here indicate that the MRU method is highly effective at recovering injured E. coli O157:H7 from beef carcass samples. The MRU method also is effective for recovery of E. coli O157:H7 from hide samples, however incorporating IMS buffer or PBS-CHAPS as the wash buffer improves the ability to correctly identify positive samples (when interference by background microflora is expected). Finally, the MRU method for recovering E. coli O157:H7 from feces is substantially improved by the incorporation of a phosphate buffer in the TSB enrichment broth.