GB virus-B (GBV-B) is a member of the Flaviviridae family of viruses. This RNA virus causes acute resolving hepatitis in experimentally infected tamarins, but its natural host remains unknown. GBV-B and a related virus, GBV-A, were recovered from serum containing the "GB agent," which was believed to have originated from a surgeon (initials: GB) with acute hepatitis. GBV-B has special interest because it is the virus related most closely to hepatitis C virus, which is an important cause of acute and chronic liver disease in humans. In the present study, we found that the host range of GBV-B includes owl monkeys. Tamarins and owl monkeys belong to two different families of New World monkeys. The natural history of GBV-B in the two owl monkeys studied was similar to that previously found for tamarins and was characterized by early appearance of viremia and viral clearance. However, the peak viral titers of GBV-B observed in owl monkeys (10(5) genome equivalents [GE] /ml) were lower than those observed in experimentally infected tamarins (10(7)-10(8) GE/ml) and acute hepatitis was observed in only one animal. If GBV-B were indeed a virus of humans, it would be expected to infect chimpanzees, a surrogate of humans, because all recognized human hepatitis viruses are transmissible to chimpanzees and cause hepatitis. However, in the present study, we failed to transmit GBV-B to a naive chimpanzee. In addition, a second naive chimpanzee transfected intrahepatically with RNA transcripts from an infectious clone of GBV-B did not become infected. Thus, chimpanzees are apparently not susceptible to GBV-B. Finally, we failed to detect GBV-B in acute-phase serum from surgeon GB. Our data suggest that GBV-B is not a human virus and that GBV-B, like GBV-A, is a virus of New World monkeys.