The ability of Campylobacter jejuni (83 strains) and C. coli (17 strains) to metabolise pyruvate was assessed in vitro using oxygen electrode system. All the strains tested were able to oxidise pyruvate. However, C. jejuni and C. coil have marked differences in the oxidation rates of pyruvate. Whereas C. coil strains oxidize pyruvate at a constant, high rate with high affinity, C. jejuni displayed a low rate at lower concentrations, but at higher concentrations the rate and affinity increased. In the presence of an inhibitor (of -flouropyruvate), pyruvate oxidation was abolished completely in C. coil but only partly in C. jejuni. Preliminary molecular studies indicated a significant variation in nucleotide composition of the genes involved in pyruvate metabolism between C. jejuni and C. coli. It is, therefore, possible that C. jejuni strains may have more elaborate pyruvate metabolism pathways than that in C. coli. This has probable consequences on the inability of C. coli to survive under stressful conditions and thus may explain the differences in the occurrence of this organism and C. jejuni.