In 1976 two kilns with numerous wasters of ornamented tiles were excavated at Bistrup near Roskilde. Identical ornaments had earlier been found on floor tiles from seven locations, mainly churches, in and around Roskilde and also as far away as OrC9 and Asnäs. The question arose whether all the tiles showing these ornaments had been made at Bistrup, or whether the tiles used in the more distant churches could have been made locally by travelling craftsmen. A neutron activation analysis project was set up with the purpose of comparing tiles found in the churches with local clay sources and with wasters from Bistrup. Until this time, tiles and clay from five locations have been compared: two groups of wasters from Bistrup, a church in Roskilde (St. Laurentius), the OrC9 church, and local clay from OrC9. A statistical treatment of the data by a stepwise discriminant analysis indicated that the tiles from St. Laurentius were compatible with the wasters at Bistrup; whereas the tiles from OrC9 matched neither the wasters nor the local clay from OrC9.