We report on the infrared spectroscopic characterization of microstructured self-assembled monolayers by scanning near-field infrared microscopy. Using a CO laser as the radiation source in the characteristic amide band (at 1711 cm-1 (λ = 5.85 μm)), we were able to image self-assembled monolayers of thiols. The measurements were carried out on well-defined microcontact printed line patterns of monomolecular films of 1-octadecanethiolate and biotinylated alkylthiolate (BAT). The lateral resolution was 90 × 90 nm2, which is well below the Abbe limit. The detection limit was 5 × 10-20 mol corresponding to 27 attogram or 30 000 molecules of BAT. This demonstrates the high sensitivity of our setup, which allows recording IR spectra of a single monolayer.