A nonbioluminescent bacterium symbiotically associated with the insect-pathogenic nematode Heterorhabditis spp. 86H1 was isolated in China. Both of two forms exhibited antibiotic activity, but only primary form enhanced nematode production. Using the EMB agar. the two forms were easily distinguished. According to its morphological, cultural, physiological, biochemical and serolo-gical characters, it was identified as Xenorhabdas luminescens. So the characterization of the species may need to be amended to allow for bioluminescense or not.