The photochemical reactions of phenazine and acridine adsorbed on silver colloid surfaces were studied. Both molecules, when adsorbed on the surface of colloidal silver, were found to photodecompose with the cleavage of a N-C bond in a one-photon process. Phenazine was found to photodecompose further to graphitic carbon under our experimental conditions, particularly when irradiated with short-wavelength laser light. The reaction rate of phenazine, which we propose to adsorb flat on the surface, was faster than that of acridine, which we suggest adsorbs standing up, implying that the reaction rate might depend on the orientation of the molecule with respect to the local metal surface. The reaction rate and degree of photodecomposition of these compounds depend on the irradiation wavelength in a complicated manner. For acridine, the photoreaction rate and the Raman enhancement increased toward the blue, whereas the degree of photodecomposition, i.e., the quantity of photoproduct produced, is a maximum at similar to 500 nm.