Two trials were performed to test the stability and efficacy of a commercial enzyme preparation containing xylanase and protease activities to pelleting. In Trial 1, 576 male Cobb chicks were fed wheat-based diets to 21 d with or without enzyme and pelleted after conditioning for 55 or 140 s at 70, 75, 80, 85, 90, or 95 C. In Trial 2, 2,880 male Cobb chicks were fed wheat-based diets to 42 d with no enzyme, or with enzyme addition before or after pelleting with conditioning for 30 s at 70, 80, 90, or 95 C. Enzyme addition had a positive effect on BW gain and the feed to gain ratio (FG) in Trial 1 and on FG to 42 d in Trial 2. All treatment effects were significant for intestinal viscosity in both trials. Two- (BW) and three-way (BW, FG) interactions between enzyme, temperature, and time were seen in Trial 1. With enzyme supplementation, second degree polynomial equations of performance on conditioning temperature had high R2 values for BW and FG, with temperatures between 80 and 85 C being most favorable. Enzyme activity in unsupplemented diets measured in vitro was largely eliminated at temperatures above 80 C, whereas the decline in activity in supplemented diets was linear. In spite of the decline in enzyme activity measured in vitro, intestinal viscosity of chicks fed enzyme-supplemented diets remained low with high processing temperatures, whereas that of chicks fed unsupplemented diets increased dramatically.