The vibronic activity revealed by the two-photon spectra of three azines of current interest such as pyridine, pyrazine and pyrimidine, has been calculated in detail. The method used, based on the “orbital following” scheme to calculate the vibronic interaction integrals, allows for a straightforward analysis of the main contributions to the two-photon tensor. The relevant normal modes active in the low-lying excited states are determined and the main mechanisms of vibronic borrowing discussed.