Enthalpies of dissociation of four isoleucyl dipeptides having alkyl side-chains (L-isoleucine-glycine, L-Ile-Gly; L-isoleucine-L-alanine, L-Ile-L-Ala; L-isoleucine-L-valine, L-Ile-L-Val; L-isoleucine-L-isoleucine, L-Ile-L-Ile) in water at 298.15 K have been determined. Enthalpies of dilution have also been calculated. These results were used to derive the enthalpic coefficients of interactions according to the modified McMillan-Mayer's model. The results are considered in an effort to establish a possible relation between dissociation, intermolecular interactions and the size of the alkyl side-chains. (C) 2005 Elsevier B.V. All rights reserved.