A protocol based on immunomagnetic separation (IMS) and competitive polymerase chain reaction (C-PCR) was developed for quantitative detection of Escherichia coli 0157:H7 in ground beef. Internal standard sequences were synthesized by PCR with hybrid primers composed in part of original primers for C-PCR. A single concentration of internal standards was used for C-PCR after calibration with known amounts of target DNA. After a 6 h enrichment in Tryptic Soy Broth (TSB), C-PCR enabled quantitative detection of 0.5 to 5.5 CFU per gram of ground beef with Shiga-like toxin 1 and 2 (SLT 1 and 2) primers respectively.