In this study, beta -galactosidase from Kluyveromyces lactis was immobilized onto graphite surface using glutaraldehyde as the crosslinking reagent with the specific activity yield of 17% and 25%, while the enzyme loading was 1.8 and 1.1 U/cm(2) of the graphite external surface area, respectively. The activity yield was decreased with the increase of the enzyme loading. The Michaelis-Menten kinetics parameters, K-m and V-m for the free enzyme were estimated to be 1.74 mM and 77.34 mu mol o-nitrylphenol min(-1) mg(-1) enzyme, respectively. The K-m value of the immobilized enzyme was found to be of five folds of the free enzyme. Lactose hydrolysis at concentrations of 5% (w/v) by the immobilized enzyme was also investigated. The degree of Lactose hydrolysis was approximately 70% at 37 degreesC over a period of 3 h. The immobilized enzyme showed a good storage and operational stability. (C) 2001 Elsevier Science Ltd. All rights reserved.