Absorption spectra in the visible range as well as IR and Raman spectra have been obtained for congo red alone and in contact with lysine and various polylysines. Using the vibrational spectra to follow the evolution of the interaction, indications are that the dye always goes into its basic form when it interacts with the model molecules. Moreover, it appears that the interaction depends, to a certain extent, on the beta-sheet conformation of the protein.