Extrahepatic biliary atresia is a devastating disease occurring in 1 in 10 000 to 14 000 infants annually in the United States. We have recently described preliminary data suggesting an association of group C rotavirus with biliary atresia in two infants. However, a group C rotavirus animal model of biliary atresia is not presently available. On the other hand, some strains of the bettercharacterized and much more common group A rotaviruses produce hepatobiliary disease in infant mice. This disease shares many characteristics of the human infection. The present report describes extrahepatic biliary obstruction in immunocompetent BALB/c infant mice infected with a human or animal strain of group A rotavirus. Two-d-old BALB/c mice orally inoculated with hepatobiliary tropic rotavirus were shown to have active virus replication in the biliary tract and liver as early as 48 h postinoculation. At approximately 7 d postinoculation, between one fourth and one half of infant mice, depending on the virus strain, showed signs of inflammation and swelling in the bile ducts. The obstruction was complete in about one half of symptomatic animals. Although there was no obvious atresia as described in human infants, the obstruction was irreversible about 50% of the time, and the resulting fibrosis and bile ductular proliferation in the liver were strikingly similar to those seen in the liver of the human infant with biliary atresia.