The taxonomic affiliation was determined for four Xenorhabdus strains isolated from four Steinernema hosts from different countries. As compared to the five validly described Xenorhabdus species, i.e., X. nematophila, X. japonica, X. beddingii, X. bovienii and X. poinarii, these isolates represented novel species on the basis of 16S rRNA gene sequences and riboprint patterns, as well as by physiological and metabolic properties. They were named Xenorhabdus budapestensis sp. nov., type strain DSM 16342T, isolated from Steinernema bicornutam; Xenorhabdus ehlersii sp. nov., type strain DSM 16337T, isolated from Steinernema serratum; Xenorhabdus innexi sp. nov., type strain DSM 16336T isolated from Steinernema scapterisci; and Xenorhabdus szentirmaii sp. nov., type strain DSM 16338T, isolated from Steinernema rarum.