Aluminum samples have been investigated during and after exposure to well-controlled amounts of NaCl and humidified air. With infrared reflection absorption spectroscopy the deliquescence of NaCl crystallites could be followed in situ at high relative humidity (RH), as well as the growth of different aluminum oxide, hydroxide and chloride corrosion products. Investigations with scanning electron microscopy and energy dispersive X-ray analysis after exposure revealed the growth of filaments representative of filiform corrosion and chlorine enrichment in the filament heads. The exposed samples were further investigated with synchrotron based photoelectron microscopy/spectroscopy. Spectra taken of the Al 2p core level showed an intricate structure with multiple components in the core level. By means of mapping the intensity of the different chemical states within the core level the distribution of compounds over the surface could be determined. An enrichment of aluminum chloride containing compounds was found in the heads of the filaments, whereas aluminum oxides or hydroxides were observed both inside and outside the filaments. (C) 2003 Elsevier Science B.V. All rights reserved.