A modified live, canine origin parvovirus vaccine was tested for safety, efficacy, and clinical performance. The vaccine protected dogs from challenge of immunity with canine parvovirus (CPV) that caused clinical illness in all nonvaccinated dogs. Vaccinates all developed CPV serum neutralization antibody titers, with a mean value of 1,664. Challenge virus was not isolated from vaccinates, but feces from nonvaccinated dogs were CPV-positive for up to 4 days following challenge. In a pathogenicity test, dogs inoculated orally with 10 times the label dose remained clinically normal. In a reversion-to-virulence test, the vaccine strain remained nonpathogenic through 6 passages in seronegative test dogs. An immunologic interference test demonstrated that test dogs developed antibodies for all antigens in a combined canine distemper virus-adenovirus 2-parainfluenza virus-parvovirus vaccine and a Leptospira interrogans serovars canicola and icterohaemorrhagiae bacterin. A total of 1,796 doses of the multivalent preparation was administered in a field study, with veterinary practitioners reporting 36 local and 5 generalized reactions.