SINCE the eradication of smallpox in Equatorial Africa several ‘new’ pox viruses have been isolated in our laboratory from materials collected by WHO field workers—monkeypox virus from an affected individual and the ‘whitepox’ viruses from apparently healthy monkeys and rodents. Monkeypox virus is not widespread but occasionally infects man and has caused death: 33 such cases have occurred in Africa, with 6 deaths. It is not known whether whitepox viruses are pathogenic for man but by laboratory markers they are indistinguishable from variola virus1. We report here that a whitepox virus identical to the whitepox virus found in feral monkeys and rodents in Equatorial Africa has now been isolated from the kidney and lungs of golden hamsters with an asymptomatic form of infection caused by intracordial inoculation with monkeypox virus. This result supports the hypothesis that natural whitepox viruses are white clones always present in populations of monkeypox virus.