Various deposits of hydrogenated amorphous carbon (a-C:H) on silver have been studied with surface-enhanced Raman scattering (SERS). When short accumulation time was used and scattered radiation were recorded with a Raman microscope, subsequently measured spectra of a-C:H often exhibited strong fluctuations. We showed by analysing the spectral fluctuations for various a-C:H samples, that the process leading to the appearance of strong SERS fluctuations is practically insensitive to the actual structure of a-C:H clusters. The appearance of strong SERS fluctuations should be, therefore, explained by the temporal changes of the electromagnetic enhancement, rather than by the fluctuations of the resonance enhancement. (c) 2006 Elsevier B.V. All rights reserved.