The seroprevalence and, or, incidence of canine coronavirus infection was determined in several dog populations in the UK. Seroprevalence ranged from 76 per cent for a rescue kennel to 100 per cent in a commercial breeding colony. In the rescue kennel there was no difference in seroprevalence of the virus between dogs less than or more than four months of age. In the breeding colony, subclinical seroconversion occurred between six and 10 weeks of age. The virus was isolated from faecal samples from 45 of 100 dogs in the rescue kennel; it was isolated from 73 per cent of the dogs with diarrhoea and from 43 per cent of those which did not have diarrhoea. In field cases of acute, mainly haemorrhagic diarrhoea in pet dogs, eight of 32 were positive for canine coronavirus. No canine coronavirus was isolated from either clinically healthy pet dogs in a boarding kennel or from non-diarrhoeic pet dogs examined at the University of Liverpool Small Animal Hospital. It would appear that although canine coronavirus is widespread, the role of the virus in canine enteritis is still equivocal.