The diversity and distribution of entomopathogenic nematodes in the families Steiner-nematidae and Heterorhabditidae were assessed throughout an extensive soil survey in Turkey during 1999 and 2000. Entomopathogenic nematodes were recovered from six out of seven regions sampled, with 22 positive sites (2%) out of 1080 sites sampled. A single nematode isolate was recovered at each of the positive sites, of which 15 were steinernematid isolates and seven were heterorhabditid isolates representing a total of four species. Based on morphometric and molecular data, the nematode species were identified as Heterorhabditis bacteriophora, Steinernema feltiae, S. affine, and Steinernema n. sp. The most common species was S. feltiae, which was isolated from 10 sites in six regions, followed by H. bacteriophora from seven sites in five regions, S. affine from four sites in two regions, and Steinernema n. sp. from one site. Heterorhabditis bacteriophora and S. feltiae have been found in many parts of the world, whereas S. affine, so far, has only been recovered in Europe until our survey. Steinernema affine was isolated from the European (Marmara) as well as the Asiatic region ( Middle Anatolia) of Turkey. A new undescribed Steinernema sp. was isolated from the most eastern region ( East Anatolia) of Turkey. Soils of the positive sites were classified as sandy, sandy loam, or loam ( 68.2%) and sandy - clay - loam or clay loam (31.8%) and the pH ranged from 5.6 to 7.9. The habitats from which the entomopathogenic nematodes were isolated were broadly classified as disturbed (59.1%), which included agricultural fields and poplar planted for lumber and wind breaks, and undisturbed (40.9%), which included pine forest, grassland, marsh and reed sites. Steinernema feltiae, S. affine, and H. bacteriophora were recovered from both disturbed and undisturbed habitats. The new Steinernema sp. was recovered from grassland. Our survey showed that these nematodes occur widely throughout Turkey, but at a frequency below that reported for other parts of the world.