Technical Abstract: Campylobacter is the most common cause of acute bacterial gastroenteritis in humans worldwide, and poultry and poultry products are a major source of infection. Arcobacter is closely related to Campylobacter and has recently gained attention as an emerging foodborne pathogen. However, few reports have been published on the prevalence of Arcobacter in U.S. poultry plants. The purpose of this study was to optimize methods of Arcobacter isolation and culture and to compare the prevalence of Arcobacter and Campylobacter on broiler carcasses from a commercial poultry processing plant. Carcasses were sampled at three sites along the processing line: 1) pre-scalding, 2) pre-chilling, and 3) post-chilling. Samples were collected during five plant visits from September to October of 2004. For Arcobacter isolation, Houf broth followed by plating on Brucella agar supplemented with 5% lysed horse blood and cefoperazone, vancomycin, and amphotericin B (CVA) produced the best results. For Campylobacter, Bolton’s broth was used in conjunction with plating on CVA medium. CVA medium was very efficient for direct plating of Campylobacter. Overall, Campylobacter was isolated from 78.5% (255 of 325) of the carcasses from the three collection sites, while Arcobacter was isolated from 55.1% (179 of 325). Our results demonstrate significant contamination of broiler carcasses by Arcobacter although less than that found for Campylobacter.