White marble at the front of the Cathedral of Como (northern Italy) is degraded. In order to design the proper conservation treatment, it is necessary to carry out experiments on the same or similar stones. Marble samples from major Italian quarries and from the Como Cathedral have been analyzed for their trace element content, which is indicative of the provenance of this marble. Samples were submitted to neutron activation analysis to determine calcium, scandium, chromium, iron, cobalt, nickel, zinc, rubidium, strontium, antimony, cesium, barium, lanthanum, cerium, samarium, europium, gadolinium, holmium, thulium, yttrium, ytterbium, lutetium, hafnium, gold, thorium, and uranium. Results of this investigation and their precision and accuracy are discussed. Data reduction was carried out by identifying first those elements which are meaningful for discrimination purposes and then by submitting the data to cluster analysis. The data has allowed the following: characterization of the investigated marble quarries on the basis of their trace element content, identification of the provenance of the marble used in the Como Cathedral, difference in the element distribution of weathered marble samples from the same quarries. See also AATA 21-214.