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Thirty-six encoded isolates of Escherichia coli, 32 of which were of serotype O157. were examined by pyrolysis mass spectrometry (PyMS). Thirty-one of the serotype O157 isolates possessed the flagellar antigen H7 and produced Verocytotoxin (VT). the other isolate serotyped as H45 and was non-toxigenic. Eighteen of the VT-producing E. coli (VTEC) isolates were from sporadic disease in residents of the Northern Region. Standard principal component (PC) and canonical variate (CV) analysis of the data distinguished only the four non-O157 isolates from the remainder which were indistinguishable by this approach. A similarity matrix based on differences between individual CV means distinguished a further ten isolates. The matrix correctly clustered 2 pairs of isolates from siblings and 4 isolates from an affected family. A further 5 clusters of 3 or more isolates and 6 pairs of isolates were defined. These groupings proved to be homogenous for toxin phenotype but occasionally entrained isolates of dissimilar phage type. However, in general, PyMS-derived clustering of apparently sporadic isolates accorded with geographical locations as determined by postcode. PyMS, which is a quick and high volume capacity phenotypic technique. may be a useful addition to existing methods in the investigation of the epidemiology of sporadic VTEC disease.