When estimating the degree of oxygen tolerance of Campylobacter spp. on Brucella medium, the brand of tryptone (pancreatic digest of casein) used in the medium greatly influenced the results. In fact, with some brands and batches of tryptone, C. jejuni could grow at 21 % O₂ without any additional scavengers of reactive oxygen intermediates (ROIs), although CO₂ was still required for growth. When the medium was prepared with other brands of tryptone, it did not allow growth of C. jejuni beyond 10% O₂. The dependence of the growth response on different types and brands of tryptone-based media makes it impossible to achieve reproducibility in oxygen tolerance studies. To eliminate such variation in complex media, we developed a chemically defined medium for Campylobacter spp. This medium allows reproducible colony counts to be obtained. The medium was used to assess the effect of ROI scavengers on the oxygen tolerance of various Campylobacter species. Allopurinol, azelaic acid, caffeine, cimetidine, and pyruvate when used singly were the most effective in enhancing oxygen tolerance. When ROI scavengers were combined with dimethyl sulfoxide, the effects of allopurinol, azelaic acid, caffeine, cimetidine, and pyruvate were even more pronounced than when they were used alone. A combination of tetramethylpiperidine-1-oxyl (1EMPOL), a superoxide dis mutase mimic, with pyruvate also enhanced oxygen tolerance effectively. A survey of the literature dealing with the types of ROIs destroyed by scavengers used in our study suggests that hydrogen peroxide (H₂O₂) and hydroxyl radicals (OH.) are the most toxic ROIs for Campylobacter species. / Master of Science