The endophytic fungus Acremonillm coenophialum Morgan-Jones & Gams conveys resistance to herbivory in tall fescue, Festuca arundinacea Schreber. In contrast, nitrogen fertilization generally enhances plant quality for herbivores. We studied the in effects and interaetion of A. coenphialum and fertilization on plant-feeding, predatory, and soil-dwelling invertebrates in tall fescue turf. Fall armyworms, Spodoptera frugiperda (J. E. Smith), developed faster when reared on foliage from plots treated with medium or high rates of urea than on unfertilized tall fescue, but development rates were not affected by A. coenophialum. Greenbugs, Schizaphis graminum Rondani, preferred fertilized, endophyte-free fescue over nonfertilized, endophyte-free grass. Similarly, bird cherry-oat aphids, Rhopalosiphum padi (L.), developed fastest on fertilized, endophyte-free tall fescue. Fertilization, however, did not overlide the strong, adverse effects of A. coenophialum on both aphid species. In field plots, densities of leafhoppers, flea beetles, and Staphylinidae were generally higher in fertilized than in nonfertilized turf. Flea beetles and two of the five most abundant species of leafhoppers were less numerous in endophyte-infected plots. Predatory arthropods, earthworms, oribatid mites, and Japanese beetle grubs were equally abundant in endophyte-infected and endophyte free plots. Fertilization did not affect the densities of oribatids or P japonica, but earthworms Were more abundant in fertilized plots on some dates. Results showed variable main effects, and an absence of interactive effects of A. coenophialum and fertilization on invertebrates in tall fescue. Fertilization of tall fescue probably will not nullify the benefits of endophyte-enhanced resistance.