Mucosal biopsies from canine jejunum and ileum were established in organ culture, and remained structurally intact for up to 72 hours. Infection of such mucosal biopsies with an enteropathogenic Escherichia coli (EPEC) 0111 results in the characteristic loss of brush border observed during natural and induced infection in other animal species. Within four hours of infection, bacteria had become attached to the mucous overlying the microvilli and by eight hours had penetrated between the microvilli resulting in partial loss of the brush border. After 24 hours incubation there was almost complete effacement of the brush border with cup and pedestal formation at sites of bacterial adherence. We conclude that EPEC should be considered as a potential cause of diarrhoea in the dog and that organ culture of canine mucosal biopsies provides a useful model for studying infection with EPECs and other enteric pathogens.