Ten out of 18 babies at risk developed enteritis in an outbreak in a special-care baby unit. Salmonella, Shigella, and Escherichia coli belonging to the traditional infantile enteropathogenic serogroups were not found in faeces from the babies and the staff, and no virus particles were found by electron microscopy. Detailed serotyping of E. coli showed that five of the 10 babies with diarrhoea and one of the eight without diarrhoea were excreting E. coli O6.H16. All six isolates of this serotype produced both heat-labile and heat-stable enterotoxin. Enterotoxigenic strains of E. coli O6.H16 have caused outbreaks of enteritis in adults in the USA and Japan.