The fast development of the world's bioethanol industry initiated debates on "food versus fuel" and the industry's environmental impact. Lignocellulosic biomass does not compete with food crops because it utilizes waste resources: however, the processing of a renewable energy source usually involves the consumption of non-renewable resources. To justify the production of second generation biofuels it is necessary to confirm that the energy produced from the lignocellulosic biomass is greater than the energy consumed in the ethanol production. The exergy analysis provides a unified and effective tool for the evaluation of the global process efficiency. This methodology requires an analysis of each stage of the production process. In this work, the stage of enzymatic hydrolysis was chosen as a case study because it is a decisive step in production process performance. The exergy analysis concept has been applied to evaluate two types of enzymatic hydrolysis reactors of lignocellulosic biomass for the production process of second generation bioethanol fuels from renewable resources, with the support of ASPEN-HYSYS (R) and other software developed by the authors. (C) 2009 Elsevier B.V. All rights reserved.