Enteropathogenic Escherichia coli strains are a common cause of infantile diarrhoea but do not produce recognised enterotoxins. Three strains of proven virulence were examined for toxins which may be missed in conventional tests. Cell lysates and concentrated culture supernates of organisms grown in five different media gave negative results when examined for adenylcyclase stimulating activity. The additions of zinc ions or lincomycin to these media or the use of iron-depleted media also gave negative results. The significance of these findings and the possible role of other toxins in diarrhoea due to enteropathogenic E. coli are discussed.