Surface enhanced Raman scattering (SERS) spectra of pyrazine (pz) adsorbed on a silver electrode from aqueous solutions containing either 1.0 M KCl or 1.0 M KBr are presented. The SER spectra display bands which are usually forbidden in the normal Raman spectrum of pz. The presence of these forbidden bands and the orientation of the molecules on the electrode surface are discussed under the two most accepted surface enhancement theories : the charge transfer and the electromagnetic model, The dependence of SERS intensity of several pz vibrational modes on the applied potential (potential profile) is also presented for different pz concentrations and excitation wavelengths. SER spectra, obtained at potentials more negative than -900mV (vs. SCE), contain new bands due to reduction of the pz molecule. It is clear that some of these products of decomposed pz remain trapped on the electrode surface, and this can lead to misunderstandings of the interpretation of the adsorbed pz spectrum. Several controversial aspects presented in the literature about the surface Raman spectrum of pz are clarified and discussed.