Tall fescue (Festuca arundinacea Schreb.) is a common pasture grass adapted to a wide range of environmental conditions. An endophyte, Acremoninm coenophialum Morgan‐Jones & Gams, growing in association with tall fescue is known to produce ergopeptine alkaloids that are thought to be detrimental to animal health. Endophyteinfection changes how tall fescue plants grow and may be involved in the adaptability of tall fescue to environmental extremes. The objective of this study was to determine whether plant‐endophyte associations that had previously tested as high and low ergopeptine alkaloid producers varied in competitive ability when their endophytes were removed. Two identical field studies were conducted on a Cecil sandy clay loam and a Pacolet sandy clay loam soil (both clayey, kaolinitic, thermic Typic Hapluduits) in 1987 and 1988, respectively. In each study, a modified Nelder's design was used to test the competitiveness between infected and noninfected forms of two tall fescue genotypes. Endophyte‐infected plants were larger and, generally, more competitive in mixtures with noninfected plants. When infected with endophyte, the high ergopeptine alkaloid‐ producing genotype of tall fescue had similar or reduced competitiveness than the low‐alkaloid genotype when compared with their noninfected forms. We conclude that if ergopeptine alkaloids can be genetically removed from tall fescue‐endophyte associations, the competitiveness of the plant would be unaffected in nongrazed conditions. Reduction or elimination of ergopeptine alkaloids would help improve animal health when consuming endophyte‐infected tall fescue forage.