The immunological responses to commercially available polyvalent vaccines in dogs were examined. There was a tendency in decreased lymphocyte counts on day 7 in the puppy and adult dogs. There was a significant increase in the blastogenesis of lymphocytes on day 7 and 21 in puppies, whereas no significant changes were seen in the adult dogs. Delayed type hypersensitivity (DTH) responses to phytohemagglutinin (PHA) and canine parvo-virus (CPV) vaccine monitored 0, 3, 8 weeks after vaccination produced strong reactions, in particular those to CPV vaccine rose significantly after vaccination and maintained the higher responses for at least 2 months. Therefore, it is considered that vaccination is immunomodulative rather than immunosuppressive and that DTH responses to PHA and CPV vaccine are helpful to monitor non-specific and specific immune functions in vivo.