The energetics of protonation and hydrogen-bonded complex formation between the base and its conjugated acid (homoconjugation) of pyridine N-oxide and its selected derivatives was investigated by means of Restricted Hartree-Fock (RHF) and Moller-Plesset (MP2) ab initio calculations. It has been found that introducing the d polarization functions (the 6-31G* basis set) is required to reproduce correctly the geometry of the N-O bond. The proton-transfer energy surface in the homoconjugated cations exhibits a double minimum, with 2.4 kcal/mol energy barrier for the pyridine N-oxide homocomplex; this barrier vanishes when the thermodynamic correction is included. The protonation and homoconjugation Gibbs free energies computed in vacuo correlate well with the acid dissociation and cationic homoconjugation constants determined in acetonitrile.