Using pH potentiometric measurements, concentration quotient and thermodynamic acid dissociation constants were determined for the dissociation of 2-pyridinium carboxylic acid. The determinations were carried out in aqueous media at five temperatures ranging from 20 degrees C to 55 degrees C and at two ionic strengths (I = 0.10 mol dm(-3) and I = 0.25 mol dm(-3)). Standard enthalpies and entropies of the dissociation reaction were also obtained. At 25 degrees C, the thermodynamic values of these properties are pK degrees = 0.8401+/-0.006, Delta H degrees = (-0.68 +/- 0.23) kJ mol(-1), and Delta S degrees = (-18.4 +/- 0.8) J mol(-1) K-1.