Investigation of the interactions between pyridine derivatives and model compounds of protein, as dipeptides and oligopeptides, is of special interest for pharmaceutical applications. Studies on physicochemical properties of their aqueous solutions play key role in understanding the nature of molecular interactions in liquid mixtures. Here the calorimetric method was used to measure the enthalpy of mixing in aqueous solutions of the dipeptide L-carnosine with the drug isonicotinic acid. The data were analyzed based on the McMillan–Mayer theory to obtain the cross-pair interaction coefficient, h_xy, that indicates relatively strong interactions with predominant hydrophilic specific interactions.