A series of studies were performed to determine the effects of arabinoxylan (AX) in western Canadian barley on the performance and digesta viscosity of young broiler chickens. Breeder lines and cultivars from the 1991 Western Canadian Barley Cooperative Program were surveyed, using a modification of the orcinol technique, to determine the range in total, water-soluble and acid-soluble AX concentrations expressed by modern genetic materials. The six-rowed barley type contained greater total, acid-soluble and water-soluble AX than hulless or two-rowed cultivars (P<-.01). The AX in hulless barley was less than the total, greater than the water-soluble (P<0.01), and not different from the acid-soluble (P<0.05) level of corresponding fractions in two-rowed barley. A genetic effect on AX concentration was seen for all cultivar and breeder line fractions (P<0.05). Envirnoment also contributed to the variation in water- and acid-soluble AX content (P<0.05). Broiler chicken diets were formualted from cultivars with high (Stacy), moderate (Manley) and low (CDC Richard) water- and acid-soluble arabinoxylan, and supplemented with purified xylanase (PX) or B-glucanase-free xylanase (XBG) at 0, 475 or 950 IU/kg. Birds consuming the PX-supplemented Stacey-based diets had increased weight gain (P<0.05) and feed conversion (P<0.05 for 950 IU/kg), with a corresponding reduction in proximal (PSIV; P<0.05). Other cultivar-xylanase combinations reduced DSIV (P<0.05), but did not affect chick performance or PSIV. The results indicated that xylanase supplementation of barley-based diets, which contain elevated soluble AX, can improve the performance of young broiler chickens consuming these diets, and that the effect is associated with reduced PSIV.