An unusually low frequency (near 2820 cm(-1)) C-H stretching band of methylene groups was detected using the SERS technique at the initial stage of formation of self-assembled monolayers on Au and Ag substrates from bifunctional alkanethiol molecules containing indole and phenol ring terminal groups. Based on the sensitivity of the band parameters to the nature of the substrate, potential and temperature, the observed band was attributed to the vibration of -CH(2) groups directly contacting the metal surface.