Strong dependence of the surface-enhanced infrared spectroscopy (SEIS) on the nature of the substrate and the surface roughness were demonstrated. Surface-enhanced vibrational spectroscopy involves the study of molecules adsorbed on surfaces that can enhance the absorption and emission of electromagnetic radiation. Self-assembled monolayers (SAM), alkanethiols on gold and silver surfaces, were prepared by dipping the silver-coated samples in 1 mM solutions of the thiols in absolute ethanol for 12 hours. SEIR spectroscopy was applied successfully to the study of monolayers adsorbed on metal surfaces in reflection absorption ATR as well as in transmission geometries. The surprisingly high enhancement was observed for the IR spectra for SAM grown on Ag/Al suggesting a simple method for the preparation of SEIR active substrates. The spectra were acquired using standard detection systems in a commercial analytical spectrometer without additional preparation.