The mode of expression of cellulase activity obtained by viscosimetric measurement is analysed. After testing different types of substrates, it appears that the best one is hydroxyethylcellulose used at a high degree of polymerisation and a high concentration. Comparison of results obtained with cellulases from Trichoderma viride and extracted from Pisum sativum favours the validity of the determination proposed. Possible physiological significance of the measurements of cellulase activity is also discusse
