This work re-examines the idea that xyloglucans of the primary cell walls of graminaceous monocotyledons differ from those of most other higher plants in lacking alpha-L-fucose residues. Suspension-cultured cells of Festuca arundinacea Schreber (tall fescue grass) incorporated exogenous L-[1-H-3]fucose into cell wall material. About 67% of the phenol-insoluble H-3 could be extracted from these cell walls with 3.6 M KOH. About 40% of the KOH-extracted H-3 was converted into products of apparent molecular weight similar to 200-2000 by Trichoderma cellulase, and a discrete peak of this material eluted from Bio-Gel P-2 at K-av 0.40 suggesting a nonasaccharide. On paper chromatography in two solvent systems, and HPLC on amino-silica, about 33% of the 3H in this fraction co-migrated with an authentic nonasaccharide, Glc(4)Xyl(3)GalFuc (XXFG), which is generated from dicotyledonous xyloglucan by cellulase digestion. In addition, the [H-3]nonasaccharide from Festuca and authentic XXFG yielded identical products when subjected to limited digestion with the fungal glycanase mixture, Driselase. Taken together, the evidence indicates for the first time that grass cell walls contained a small amount of fucosylated xyloglucan.