The objective of this study was to describe observations from cases of enteric colibacillosis in the dog. Thirteen cases of canine enteric colibacillosis were diagnosed from routine necropsy submissions to our diagnostic laboratory from 1980 to 1992. In all cases there was a clinical history of gastrointestinal disease associated with histological and bacteriological evidence of either attaching and effacing Escherichia coli (AEEC) or enterotoxigenic Escherichia coli (ETEC) infection. Of these 13 cases of enteric colibacillosis, 12 were associated with AEEC and one with ETEC. Eight of the 12 AEEC isolates were available for study. They were of various serogroups, non-hemolytic, and negative for the genes coding for fimbrial antigens F4, F5, F6, F41 and F165; enterotoxins STap, STb and LT; and verotoxins VT1 and VT2. These eight isolates were EAE-positive (E. coli attaching and effacing) by colony hybridization; six of these were also EAF-positive (EPEC adherence factor), and six were BFP-positive (bundle-forming pilus). The ETEC isolate was negative for the EAE, EAF and BFP determinants and for the fimbrial antigens tested but was positive for the STap and STb genes. Most of the dogs affected with enteric colibacillosis originated from kennels and pet shops and were aged between 1.5 and 3 months. Coinfection with other enteric pathogens was identified in eight of these 13 cases. This study showed that Escherichia coli should be considered of causal significance when investigating diarrheal disease in dogs, particularly in puppies.