Endoglucanase V catalytic core is a single chain protein of 213 amino acids. The titration of the ionizable groups of the macromolecule has been performed by an isothermal calorimetric technique and the pK(1)(0) and Delta H-1(0) related to the groups have been estimated and no apparent abnormality was observed in the titration behavior. These values are in agreement with the expected theoretical ones.