We have made calorimetric determination of enthalpy change values related to proton dissociation processes (for a series of dipeptides having alpha-alanine as first common term) of the free alpha-amino groups belonging to the amino terminal residue (N-terminal) and of the free alpha-carboxyl groups belonging to the carboxyl terminal residue (C-terminal). These values were subsequently compared with those related to proton dissociation processes of the corresponding groups of alanyl-alanine and of the individual free alpha-amino acids. The results were interpreted in terms of reciprocal influence of the components of the dipeptides.