Tall fescue (Festuca arundinacea Schreb.), through its mutualistic association with Neotyphodium endophytes, can suppress soil nematode populations, thereby promoting host vigor and drought tolerance. Information is needed on the ability of endophytes that lack livestock toxins to suppress soil nematode populations when used in novel associations with tall fescue. Soils in replicated pastures at Fayetteville and Hope, Arkansas, were surveyed for nematodes by compositing 20, 1.9-cm diameter x 10-cm deep core subsamples per fescue-endophyte association. Treatments consisted of tall fescue containing various strains of toxic or nontoxic endophytes.  Nematodes were extracted, counted, and identified to genus. The only significant effect (P<0.013) occurred at Hope, in that strains exhibited differences in soil numbers of spiral nematode (Tylenchorynchus spp.). The spiral nematode numbers in the endophyte-free (E-) control were intermediate in the range, and not different from the experimental endophyte strains. All numbers of potentially pathogenic nematodes were considered low, which limited the ability to detect endophyte strain effects. A greenhouse trial was conducted in which pots of tall fescue containing nontoxic strains of endophyte were inoculated with root-knot nematode (Meloidogyne marylandi) eggs to test the ability of 7 nontoxic strains of endophytes to deter nematode reproduction. Endophyte-free and toxic wild-type endophyte treatments were included as controls. Nematode numbers in roots of E- plants increased from the inoculation level over 9 weeks, demonstrating high nematode susceptibility. All 7 nontoxic strains caused significant reductions (P<0.01) in recoverable nematode numbers to levels similar those of the toxic endophyte. These results indicate that all endophyte strains tested possess nematode-deterring qualities and would thus be promising candidates for use in improved cultivars. Greenhouse screening using M. marylandi allowed better expression of the endophyte benefit in nematode deterrence than the field surveys, which relied on natural infestations, which were very low.