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Campylobacter jejuni is an important human pathogen. It is the primary cause of acute gastroenteritis in the United States with an estimated 2-10 million cases annually. C. jejuni is a commensal colonizer of the avian intestines and contaminated poultry is the primary source of human infection. C. jejuni has a unique metabolism and respiratory chain which offer possible targets for antimicrobials. This research project explores the physiological role of hydrogenase in C. jejuni. C. jejuni contains an uptake hydrogenase that oxidizes H2 at approximately 40 nmols H2 oxidized/min/108 cells. H2 permits growth beyond C. jejuni's microaerophilic limits. In serum bottles containing 25% O2 and 10% H2 wild-type C. jejuni reaches a terminal OD600 of .695 while cells grown at 25% O2 are unable to grow and have a terminal OD600 of .0035. The ability to grow at high O2 atmospheres supplemented with H2 does not occur in a mutant strain deficient in hydrogenase activity. Hydrogenase could offer respiratory protection to O2-sensitive enzymes. Growth under H2 -supplemented atmospheres also enhances growth rate. Wild-type C. jejuni grown in batch culture without H2 had a generation time of 1.8 hours while cells grown in the presence of H2 had a generation time of .96 hours. Mutant C. jejuni, unable to oxidize H2, did not show such a drastic reduction in generation time. The ability of wild-type and mutant C. jejuni to colonize the avian intestine were compared and no significant differences resulted. Overall it appears H2 is an efficient supplemental source of energy that may provide a competitive advantage in the avian intestine.