Surface-enhanced Raman spectra of bipyrazine adsorbed on silver colloids were obtained and compared with those measured on Ag electrode at different potentials. The spectra were interpreted on the basis of normal mode calculations using the argentous bipyrazine coordination complex as a model to describe the absorbate-substrate interactions. It was found that bipyrazine assumes different adsorption geometries at the silver surface, either in aqueous colloidal dispersion after addition of chloride anions or on Ag electrodes at 0 potential. The SER data suggest the presence of two coexisting chemisorbed species, identified by normal mode calculations as bipyrazine bound to silver substrate through the nitrogen atoms located in "ortho" or "meta" position with respect to the inter-ring C-C bond.