The presumed high cost of cellulase enzymes is seen as a major economic hurdle in ethanol fuel production from lignocellulosic biomass. One way to reduce enzyme cost is to use much less enzyme per unit of biomass hydrolysed. The ammonia fiber explosion (AFEX) process produces a highly reactive biomass but the relationship between AFEX treatment conditions, enzyme loadings and hydrolysis yields has never been thoroughly explored. We report here the effects of AFEX treatment on the initial rates and 24 h hydrolysis yields for several crop residues and lignocellulosic materials using low enzyme levels (1-5 IU/g dry biomass). Near theoretical sugar yields are obtained for some AFEX treatment conditions at 1 IU/g for corn fiber and 5 IU/g for switchgrass. implications of the experimental results are discussed. (C) 1996 Elsevier Science.