Reovirus type 1, known to be a cause of systemic and intestinal disease in mice, is secreted into the bile of adult A/J mice after viremia. Virus found in the bile in concentrations higher than those in blood may indicate that reovirus type 1 is actively transported into the bile. The transport of virus was independent of levels of virus-specific immunoglobulin A antibody. Modifications of the virus that occurred during transport did not discernibly affect the infectivity of the virus. Entry of virus into the bile may be an important mechanism by which an enteric virus that produces systemic disease reenters the intestine for transmission.