Thin amorphous alumina films were prepared on stainless steel, type AISI 304, by low pressure metal-organic chemical vapour deposition. The effect of thermal annealing in nitrogen (for 2, 4 and 17 h at 600, 700 and 800 degrees C) on the film properties, including the protection of the underlying substrate against high temperature corrosion and the chemical composition of the film, were investigated. Corrosion experiments performed at 450 degrees C in a hydrogen sulphide-containing gas, showed that the thermal annealing process had a detrimental effect on the protective properties of the alumina films. From FTIR and Auger measurements, it was found that the amorphous alumina, containing boehmite, converted to gamma-alumina during the annealing process.