Calorimetric data are reported on the enthalpy of neutralization of polygalacturonic acid obtained during its neutralization by either tetraalkylammonium or alkaline hydroxide solution. Thermometric curves are evaluated and discussed in terms of six equivalent equations, and the successive enthalpies of neutralization of previously chosen oligomeric subunits of polygalacturonic acid are determined. Together with the potentiometric data, this information provides a complete thermodynamic picture of the effect of the size of the alkyl group and the nature of the counterion on the dissociation behaviour of the polyacid in dilute aqueous solutions.