We evaluated the effect of endophyte infection in the two turfgrasses tall fescue (Festuca arundinacea Schreber) and strong creeping red fescue (F. rubra L. ssp. rubra) on the susceptibility of three white grub species to the entomopathogenic nematode Heterorhabditis bacteriophora Poinar. Endophyte infection in strong creeping red fescue (only tested under greenhouse conditions) had no effect on nematode-susceptibility of third-instar oriental beetle (Exomala (=Anomala) orientalis Waterhouse) and northern masked chafer (Cyclocephala borealis Arrow). In tall fescue under greenhouse conditions, endophyte infection had a weak and variable enhancing effect on nematode-susceptibility of second- and third-instar E. orientalis and no effect on nematode susceptibility of third-instar C. borealis and Popillia japonica. However, under field conditions with natural white grub populations, endophyte infection in tall fescue had no significant effects on nematode efficacy against E. orientalis, P. japonica, and C. borealis. While it is possible that stronger interactions between endophytes and nematodes may occur with different grass species, cultivars, and endophyte strains, nematode-endophyte interactions appear to be too variable to allow predictions on nematode efficacy based on turfgrass endophyte status.