Small samples of various areas of the frescoes by Giotto in the Scrovegni Chapel were removed for scientific examination at the Conservation Center, Institute of Fine Arts, New York University and at the Brookhaven National Laboratory. These include samples of a white surface deposit, and goodand deteriorated paint and plaster from various parts of the Chapel. Microscopic examination showed the good plaster to be an agglomeration of small mineral particles and sand, marble chips and fine crystalline calcium carbonate. In addition deteriorated plaster contained gypsum (calcium sulphate dihydrate). Emission spectra in the ultraviolet range showed the presence of calcium and silicon (major) and aluminum, magnesium and iron (minor) and various trace impurities. X-ray diffraction measurements revealed the process of decay showing that gypsum (calcium sulphate dihydrate), was present in all deteriorated plaster and absent in good plaster. The white surface deposit proved to be almost pure gypsum. The sulfur that had combined with the calcium carbonate to form the gypsum comes from oxides of sulfur present in the air. The concentration of these oxides in the atmosphere at Padua had been measured by members of the Institute of Engineering of the University of Padua in a four-year study and are of sufficient concentration to cause this chemical change in the plaster. In order to halt the attack of sulfur oxides on the supporting lime plaster it is suggested that the paintings be isolated from such sulfur oxides, preferably by some air purification process. In other instances where similar attack is occurring and air purification is not practical, it is suggested that transfer of painting surface to a new inert support by the <i>strappo technique might be most feasible. -- AATA