Differences in hydrolysis behaviour between lyocell and viscose type regenerated celluloses (viscose and modal) have been evaluated by the study of the enzymic hydrolysis by cellulases. Kinetic parameters (V-em and k(e)) and enzyme catalytic specificity were calculated during cellulase processing. The results show low adsorption, catalytic specificity and rate of hydrolysis (V-em = 0.407 h/l h) of lyocell fibres ahead of the viscose-type fibres due to their higher orientation and crystallinity. Fibrillation treatment of lyocell favours cellulase attack by greatly increasing the availability of sites for enzyme adsorption. (C) 2003 Elsevier Science Ltd. All rights reserved.