The causes of deterioration of the gilded bronze doors of the Baptistery in Florence have been examined and the mechanism of corrosion discussed. An apparatus for thermal conditioning has been proposed and tested either on the north door of the Baptistery, or on samples exposed to the urban atmosphere in Milan and by laboratory tests on an electrochemical model. The effectiveness of the proposed apparatus has been veri fied by weight losses, by assessing soluble salts, by visual observations, by local chemical microanalysis, by monphological examinations with a scanning electron microscope equipped with an x-spectrometer and by x-ray diffraction.