Enthalpies of dilution of binary aqueous solutions containing monocarboxylic acids and monoalkylamines have been determined by microcalorimetry at 298.15 K. Pairwise self-interaction coefficients of the virial expansion of the excess enthalpies were evaluated and compared with those obtained for alkan-1-ols. The values of the coefficients are positive and increase differently with increasing number of carbon atoms on the alkyl chain, depending on the nature of the functional groups. For all series, starting with the terms containing five methylene groups, the coefficients tend to attain a constant value. Attempting to explain this behaviour, the attention was focused on the nature of the hydration of the alkyl chain.