Fifty samples were collected from each of skinned and dressed carcasses, from each of culled beef breeding cows and fed beef cattle <18 months old at two beef packing plants A and B, and from culled dairy cows at a packing plant C. The 450 samples were collected by swabbing an area of about 1000 cm2 in the anal region of each carcass. DNA extracted from each swab was tested for the IS900 and F57 sequences of the Mycobacterium avium subsp. paratuberculosis (MAP) genome by two stage, nested polymerase chain reaction (PCR) procedures. An internal amplification control (IAC) was detected in 45 or more of each group of 50 DNA preparations. IS900 and F57 were detected in some IAC-positive preparations from all and all but one of the groups of carcasses, respectively. Of the IAC-positive preparations in each group, between 6 and 54% were positive for IS900, and between 4 and 20% were positive for F57. When preparations were tested by single stage, quantitative PCR procedures, IS900 was detected in two samples but F57 was detected in none. The MAP DNA on carcasses was probably derived from small numbers of MAP from the environment that contaminated the animals' hides.