For many years strains of Escherichia coli belonging to particular serotypes (EPEC) were a common cause of outbreaks of infantile enteritis in Europe and North America. E. coli 0142.H6 was first isolated from infants with diarrhoea in Indonesia in 1960 and a further outbreak occurred in Mexico in 1965. Between 1967 and 1972 outbreaks of infantile enteritis caused by E. coli 0142 were reported in hospitals in Scotland, England, Northern Ireland and Eire. Sporadic cases occurred in Canada in 1972 and a further outbreak occurred in Arizona, U.S.A. in 1975. Strains from all these incidents were examined by biochemical and serological methods. Their resistance to antimicrobial drugs was determined and their resistance plasmids characterized; their plasmid profiles were visualized by agarose gel electrophoresis. The cumulative evidence suggests that strains isolated in the British Isles all belonged to a single clone and were related to those isolated in Indonesia, the U.S.A. and Canada. However, the strains from Mexico appeared to be unrelated. This study demonstrates that single clones of enteropathogenic E. coli may spread throughout the world, causing outbreaks of diarrhoeal disease and acquiring resistance to antimicrobial drugs.