Canine parvovirus isolates from clinical cases of enteritis were obtained from the United Kingdom, Germany and the USA and differentiated by restriction enzyme analysis into three groups, namely CPV2, CPV2a and CPV2b. The three groups were readily identified by their HphI restriction profile. CPV2 was not prevalent in cases of canine parvovirus disease after 1986. Only two CPV2 strains (original type) were found among 110 strains isolated after 1980. In Europe the frequency of isolation of the CPV2a and CPV2b field strains was similar whereas in the USA the CPV2b strain predominated. Dogs inoculated with a vaccine strain were resistant to infection after challenge with UK isolates of CPV2a and CPV2b.