During a comparison of 16S rDNA PCR-denaturant gradient gel electrophoresis (DGGE) profiles of methanogenic archea from rumen fluid, rabbit caecum and pig feces, a unique band common to all rabbit caecum samples was observed. DGGE profiling also showed that the methanogen community from the New Zealand White adult rabbits is different and less complex than the methanogen communities from the rumen and pig feces. Small subunit ribosomal gene sequences of methanogenic archaea were subsequently retrieved from the constructed rabbit caecum 16S rDNA gene library. Results of the phylogenetic analysis indicated that rabbit caecum is inhibited by members of the genus Methanobrevibacter and is possibly one-species dominanted, because all the retrived sequences exhibited similarity values of 99% or higher. This species may well be a novel species of the genus Methanorevibacter. It belongs to a distinct phylogenetic group containing methanobrevibacter woesei, Methanobrevibacter thaueri and Methanobrevibacter gottschalkii strains isolated from animal faeces, and Methanobrevibactersmithii from the predominanting methanogen population of the human large bowel.