Major cellulase components-four endoglucanases (Endo I, II, III and IV) and one exoglucanase (Exo II)-were isolated from a commercial cellulase preparation derived from Trichoderma viride by a series of chromatographic procedures. The average molecular weights were determined by SDS-polyacrylamide gel electrophoresis. Endos I, III and IV, with M(rs) of 52,000, 42,000 and 38,000, respectively, exhibited a more random hydrolytic mode on carboxymethylcellulose (CMC) than Endo II, which has an M(r) of 60,000. Endo II showed low activity towards CMC, but out of the four purified endoglucanases this enzyme had the highest specific activity against Avicel. In the hydrolysis of H3PO4-swollen cellulose by Endos I, III and IV, cellobiose was the major product, but equimolar amounts of glucose and cellobiose were formed by Endo II. Exo II, with an M(r) of 62,000, released cellobiose as the main product in the hydrolysis of H3PO4-swollen cellulose, but glucose was negligible. The combination of Endo I, II, III or IV with Exo II resulted in a synergistic effect in the degradation of Avicel at various combination ratios of these enzymes; the specific optimum ratio of endoglucanase to exoglucanase was largely dependent upon the random hydrolytic mode of the endoglucanase. On the other hand, adsorption of cellulase components was found apparently to obey the Langmuir isotherm, and the thermodynamic parameter (Delta H) was calculated from the adsorption equilibrium constant (K). The enthalpies of adsorption of the endoglucanases were in the range of -2.6-7.2 KJmol(-1), much smaller than that of Exo II (-19.4 KJmol(-1)). This suggests that Exo II shows stronger preferential adsorption than endoglucanases, and that the enthalpy of adsorption will be effective in distinguishing endoglucanase from exoglucanase.