The genomic relatedness among 28 catalase-positive Campylobacter strains was assessed by determination of DNA base composition, by DNA:DNA hybridization followed by S1 endonuclease digestion of single-stranded DNA, and by determining the thermal stability of homologous and heterologous double-stranded DNA. The catalase-positive Campylobacter strains were shown to comprise 3 species, C. coli, C fetus and C. jejuni; each included the type strain (respectively, CIP 7080, CIP 5396 and CIP 702).