The paper presents the results of experimental infection of monkeys with virus-containing specimens from a patient with fecal-oral non-A-non-B hepatitis; the study was aimed at the determination of the possibilities of simulating this infection. Of the 8 monkeys infected with the material containing virus particles of fecal-oral non-A-non-B hepatitis 5 monkeys developed the infection manifested in virus excretion in fecal specimens, a rise in the level of serum aminotransferases, and typical histological lesions of the liver tissue. The infection could also be produced by inoculation of monkeys with virus-containing material from monkey. The above results indicate that the virus isolated from a human suffering from fecal-oral non-A-non-B hepatitis may induce in experimentally infected Macaca fascicularis monkeys a pathological process simulating viral hepatitis.