Cellulase plays a key role in biochemical conversion processes for producing fuels from lignocellulose biomass because it hydrolyzes cellulose to the fermentable sugar glucose. To further understand the performance of several commercially available enzymes, we tested the ability of Genencor’s Spezyme CP, GC220 and the recently available Accellerase 1000 to enzymatically saccharify dilute sulfuric-acid pretreated corn stover solids that had been washed or left in the hydrolysate. The enzymes were tested at various temperatures (38-54^oC), solids concentrations (5-30% w/w) and enzyme loadings (5-40 mg protein/g cellulose). A response surface methodology was used to develop an empirical model of monomeric glucose yield as a function of the four factors described above. Glucose yield was highly influenced by enzyme loading at low enzyme loadings and less severely affected at higher enzyme loadings. Increasing solids concentration had a large negative impact on glucose yields, and yields were even lower when the solids were left in the hydrolysate. Temperature was less important than the other factors. Overall, it is clear that enzymes are needed that perform better in the presence of inhibitors¯sugars being the most inhibitory compounds¯contained in dilute acid hydrolysates. The problem is further exacerbated at high solids concentrations.