Newborn white mice were susceptible to peroral (p.o.) infection with murine alphaherpesvirus isolated from free-living Clethrionomys glareolus. Death occurred within 6-8 days in animals infected with the higher virus dose of 4.8 log10 TCID50. Clinical symptoms also occurred in some animals infected with lower doses, while others developed inapparent infection as judged by presence of humoral antibodies at 60 days post-infection (p.i.). The virus was detected in the lungs, blood, liver, spleen, kidneys, heart muscle, brain and urinary bladder of sick animals. Necrotising pneumonia accompanied the replication of the virus in the epithelial cells of alveolar ducts and alveolar lining as confirmed by immunofluorescence and histological examination. Latent infection of Gasserian ganglia in the survivors was not necessarily related to the administered dose of infectious virus. Two of mother females, which had eaten their diseased offspring, became inapparently infected as proved by reisolation of the virus from trigeminal ganglion explants and by detection of specific antibodies at 60 days p.i.