Australia antigen (Au(1)) was found in the sera of 20% of 125 patients with acute viral hepatitis. It was not present in the sera of 138 patients with other diseases affecting the liver (Laennec's cirrhosis, infectious mononucleosis, hepatoma, and so on). These data indicate that the antigen is selectively associated with viral hepatitis and is not a nonspecific manifestation of liver damage.
Previously we have reported the association of Au(1) with leukemia, lepromatous leprosy, and Down's syndrome, and in 1 to 20% of some tropical populations. In these groups the antigen occurs more frequently in young males; once present, it tends to persist for long periods (years). In the acute hepatitis patients there was no significant difference in distribution between the sexes; the antigen was not found in any patient less than 19 years old, and with two exceptions it was present in the sera for short intervals (days and weeks). Host factors related to immunologic competence may be responsible for these differences.