Differences in the pathogenesis of porcine parvovirus (PPV) were shown when pregnant gilts were infected by the oral and intramuscular (i.m.) routes. By the oral route, PPV took 23-32 days to cross the placenta following infection of the dam, as compared to 15 days by the i.m. route, Successful transplacental infection occurred following oral infection of dams only in the second third of gestation, whilst i.m. infection resulted in infection of foetuses in both first and second thirds of gestation. Foetal infection resulted in death and mummification only where infection of foetuses occurred before onset of immune competence--estimated at 70 days gestation. Infected foetuses either died before onset of immune competence, or survived to mount an immune response with subsequent death or survival to farrowing. It is suggested in discussion that reproductive failure due to PPV, characterised by mummification or occasional stillbirth, is associated in nature with oral infection, and occurs only when dams are infected in the first part of the midthird of gestation.