This paper describes a study of neutron activation analyses of some medieval tiles from the North Midlands. Having established the feasibility of the method of analysis, the authors applied a number of multivariate statistical techniques to derive eleven reference groups, each consisting of tiles with similar compositions which could plausibly have originated from the same source of clay. While known kiln sites could be readily distinguished, less confidence could be placed on the results where it was suspected that several sources had been mixed. Design information on the tiles when combined with the analytical results has led to the conclusion that stamps may have been passed from one tilery to another, though in some cases the tiles themselves were moved. The reference groups have proved to be useful in the authors' continuing research on the composition of tiles from this area. -- AATA