SERS has been used to study adsorption of adenine, adenosine, adenosine 5'-monophosphate, cytidine, and cytidylyl(3' → 5')adenosine on an Ag electrode. Cytidine adsorption is promoted or suppressed by equimolarly coexisting adenosine at lower or higher bulk concentration, respectively. This would reflect the limited number of SERS-active sites on the electrode surface. Investigation of the potential-induced change in the SERS spectra of adenosine derivatives provides a clear picture for the orientational change of the adsorbed molecules.