The effects of several commercially available vaccinations pre- and post-surgery on immune responses by monitoring the blastogenic responses of lymphocytes and humoral antibody responses in dogs were examined. Twenty clinical patients presented for surgery were studied. Canine parvovirus (CPV) serum antibody titers increased by twofold or more in 17 of 20 dogs and many dogs had an increase by day 7. In 3 of 4 dogs moderate hemagglutination inhibition (HI) titers (128 to 256) at the time of vaccination increased by twofold or more. Canine distemper virus serum antibody titers in 4 of 8 dogs with HI titers (< or = 32) at the time of vaccination had increased by twofold or more. In the blastogenic responses of lymphocytes to Concanavalin A and phytohemagglutinin, most dogs responded with a slight decrease following vaccination, but no significant change was noted. No adverse reaction caused by vaccination was noted and comparatively good production of serum antibody titers (CPV especially) was seen. Vaccination pre- and post-surgery neither induce severe immunosuppression, nor potentiate the severity of concurrent disease, and did not cause inapparent infection to become clinically apparent.