Acid hydrolysis of lignocellulosic materials produces several inhibitory compounds, such as sugar and lignin degradation products, compounds derived from the lignocellulosic structure, and heavy metal ions. Their toxicity is a major factor limiting bioconversion processes that utilize hydrolyzates. The identification of these compounds and the choice of the best hydrolyzate detoxification method are important for improving the efficiency of the fermentative processes. A variety of biological, physical, and chemical techniques have been proposed to reduce the concentration of these compounds in lignocellulose hydrolyzates. However, the efficiency of any detoxification method depends both on the hydrolyzate composition, which differs according to the raw material used, and on the hydrolysis conditions employed. This review describes the effects of the inhibitory compounds on fermentation yield and productivity, as well as various detoxification methods for treating the hydrolyzates. (C) 2003 Elsevier Ltd. All rights reserved.