AbstractAfter adding cationic dyes like oxazine 170, malachite green, and crystal violet to a solution of colloidal silver sometimes an absorption band appears at wavelengths>750 nm which is neither caused by the monomeric dye nor by a coagulation of the colloid. Based on electrochemical measurements this new absorption band is assigned to a chinhydron‐like adsorption geometry of the dye. Usually this band is only observed at low concentration of the dye, whereas at higher concentration the formation of H‐aggregates occurs. There seems to be a relationship between the intensity of this band and the SERS activ