The surface-enhanced Raman scattering (SERS) spectra of pyridine have been analyzed on the basis of a resonant charge transfer (CT) mechanism. The most intense bands recorded in the SERS at negative electrode potentials correspond with the normal modes that connect equilibrium geometries of the neutral molecule and the corresponding radical anion. These normal modes have been characterized according to our previously proposed method by calculating the ab initio geometries of the molecule and its anion and then building the transformation Delta Q = L(-1)Delta R, where the vector Delta Q contains those vibrations active in SERS-CT via Franck-Condon factors, thereby providing semiquantitative selection rules for this enhancement mechanism.