Fetal sera or thoracic fluids of the abnormal fetuses from different swine farms were tested for the presence of antibody to encephalomyocarditis (EMC) virus. Sera of swine fetuses infected experimentally with EMC virus were also tested. High antibody titers ranging 1:128-4096 were detected in both field and experimental samples. Detection of the positive antibody was associated with clinical herd history of increased mummification, stillbirth and neonatal death. The results suggest that EMC virus may be a natural cause of swine reproductive failure and fetal infection can be diagnosed by detecting specific EMC virus antibody in either fetal sera or thoracic fluids.