The species Yersinia (Y.) enterocolitica consists of biochemically and serologically heterogeneous strains. A vernacular nomenclature divides these strains in 'European' and 'American' bioserotypes. We investigated six strains of each group by DNA-DNA hybridization, determination of G + C mol% content and sequence alignment studies. Based on different DNA-DNA hybridization values and the 16S rRNA gene sequences a division into two Yersinia enterocolitica subspecies is justified. We propose the names Yersinia enterocolitica subsp. enterocolitica for strains belonging to the 16S rRNA gene type represented by the Type strain ATCC 9610 and Yersinia enterocolitica subsp. palearctica for strains belonging to the 16S rRNA gene type of strain Y11 (DSMZ13030).