Levels of passively transferred maternal antibodies to three canine viruses, rabies virus (RV), canine distemper virus (CDV) and infectious canine hepatitis (ICH) virus, in serum specimens from 14 fetal pups and in serial serum specimens collected up to 45 days after whelping from 14 neonate pups were compared with levels of antibodies to these viruses in milk and sera collected concurrently from their respective dams. Radioimmunoassays using RV-, CDV- and ICH virus-specific antigens showed that sera from all fetal pups had detectable levels of antibodies to all three canine viruses and ICH neutralising antibodies were detected in sera from 10 of the 14 fetal pups. As the time after whelping increased, titres of RV-, CDV- and ICH virus antibodies measured by radioimmunoassay and ICH virus neutralising antibody tests in serially collected specimens of milk from dams rapidly decreased, while titres of the antibodies in serum specimens from newborn pups in their litters steadily decreased. Individual fetal and newborn pups with a high titre of antibody to one virus also had high titres to the other two viruses, although a wide range of titres was observed among pups in each of the litters studied. Markedly higher titres of antibody to all three viruses were observed in serially collected specimens of sera from dams than in sera from fetal and newborn pups in their litters. Results show that maternal RV, CDV and ICH virus antibodies are transferred from dams to pups in utero and by nursing. Levels of these maternal virus-specific antibodies in newborn pup sera decreased at similar rates as time after whelping increased.