Several types of viral hepatitis may exist. Hepatitis A (MS-1 type) can be transmitted to marmosets and chimpanzees. Virus-like particles, which may be parvo- or enteroviruses and which have been demonstrated in feces of this type of hepatitis, do not share cross-reacting antigens with hepatitis B but do cross-react with fecal hepatitis A antigen. Hepatitis A (GB type), which also does not cross-react with hepatitis B, is not antigenically identical with MS-1; it can be transmitted to marmosets and it may be similar to non-type A/non-type B post-transfusion hepatitis. Hepatitits B does not cross-react either with HA particles, the faecal hepatitis type A antigen or with the MS-1 or GB strains; it can be transmitted to chimpanzees and rhesus monkeys but not to marmosets.