In order to simulate the effect of atmospheric pollution on leather and parchment, an experimental caisson, in which the temperature and relative humidity were variable and the admission of gaseous pollutants controlled, was constructed. The leather was submitted to the action of the anhydride of sulphur in the presence of catalysts, oxidants, and high humidity. Parallel to this study, similar samples were suspended in a particularly polluted site in the city of Rouen and a comparative study of the alterations which occurred artificially and naturally was done.