The effect of site of supplementation of a mixture of two crude preparations (Enzyme C and Enzyme X) of exogenous polysaccharide-degrading enzymes (EPDE) was studied in vivo using four ruminally and duodenally cannulated heifers (Exp. 1). The treatments were as follows: control (no EPDE), EPDE supplied through the diet (EF, 47.0 g/d), and EPDE infused continuously into the abomasum (EA, 41.6 g/d). Enzyme treatment increased the concentration of soluble reducing sugars (P < .05) and decreased NDF content (P < .05) in the treated feed, but this did not increase the rate or extent of in sacco disappearance of DM from the feed. Compared with control, ruminal fermentation was not affected by EF, but abomasal infusion increased (P < .05) rumen ammonia levels and shifted ruminal VFA patterns. Ruminal carboxymethylcellulase (CMCase) and xylanase activities were not affected by treatment. Abomasal infusion increased (P < .05) duodenal xylanase activity as compared with control and EF, but apparent digestion of DM, NDF, and CP were not affected by treatment. Negligible levels of CMCase and amylase reached the duodenum. During an in vitro experiment (Exp. 2), abomasal stability of the two EPDE was studied over a range of pH from 3.39 to .85, with or without pepsin. Carboxymethylcellulase activity (in Enzymes C and X) and beta-glucanase activity (in Enzyme C) were largely unstable against pepsin proteolysis (P < .001) and low pH (P < .001). Xylanase and amylase activities were resistant to pepsin but irreversibly inactivated at low pH. These two experiments showed that abomasal supplementation of EPDE did not successfully supply cellulases and amylases to the intestine, due partially to their limited resistance to low pH and pepsin proteolysis. Although EPDE significantly increased the level of xylanase activity at the duodenum, this did not significantly improve total tract digestion.