The focus of this study was to determine the effect of supplementing cellulase with hemicellulase during enzymatic hydrolysis of switchgrass pretreated by soaking in aqueous ammonia (SAA) under a range of conditions. SAA was performed using 15% aqueous ammonia for 8 or 24 h at temperatures of 40 or 60 degrees C. The combined effect of cellulase and hemicellulase loadings on glucose yield during enzymatic hydrolysis was modeled for each pretreatment condition. Glucose yields greater than 85% of theoretical were achieved for pretreatment at 40 degrees C for 24 h and for 60 degrees C for 8 h. Hemicellulase supplementation was not sufficient to achieve these glucose yields at lower severity SAA pretreatment. High severity SAA pretreatment also led to low yields despite improved delignification. (C) 2012 Elsevier Ltd. All rights reserved.