Trypsin, pronase and subtilisin were immobilized on chitosan by glutaraldehyde coupling. Significant retention of activity was observed when synthetic substrates as well as casein were used. The specific activities of the bound proteinases ranged from 38% to 79% of their initial specific activities. The pH-activity profile of trypsin was slightly shifted toward alkaline values, and its thermal stability was increased. Immobilized trypsin was found to be less sensitive to its natural inhibitors than the soluble enzyme.