The effects of the N-atom protonation on the static dipole polarizability of a series of representative monocyclic azines (pyridine, pyrimidine, pyridazine and pyrazine) have been investigated using ab initio and density functional theory DFT methods. It was found that the protonation induces significant negative variations in the dipole polarizability of monocyclic azines. These variations, which are the consequence of depletion in the electronic charge of the overall molecule are linearly correlated to the azines experimental pKa. (C) 2004 Elsevier B.V. All rights reserved.