The euploid-diploid cell line CE, issuing spontaneously from a normal human bone marrow culture, displays B-cell differentiation and activation markers and is positive (> or = 90% of cells) for Epstein-Barr nuclear antigens. CE suspensions were inoculated with serum from a patient chronically infected with hepatitis C virus (HCV). After inoculation, the cells were regularly subcultured with a split ratio of 1:2 every 4-6 days. RNA extracted as late as 65 days after infection from the inoculated cells were positive by polymerase chain reaction for the 5' untranslated region of the HCV genome, and viral antigens were detected by immunofluorescence. Virus was also released from the infected cells into the medium. Intracellular HCV could be successfully passaged twice in CE cultures. On the basis of these findings, the CE cell line appears promising as a model for studying HCV replication and persistent infection in vitro.