All arthropod-borne viruses at present under study in the Rockefeller Foundation Virus Laboratories, N.Y., are readily inactivated by a 1:1000 dilution of sodium desoxycholate. The only viruses discovered to date that are resistant to the action of this bile salt are strains of human poliomyelitis, mouse encephalomyelitis, Coxsackie and encephalomyocarditis viruses.