ABsAg surface antigen was detected, on enterobiopsies at duodenal level by means of Crosby capsule, in 12 subjects with various types of hepatitis B and in 2 control subjects, by means of immunofluorescence. The antigen was present in the duodenal mucosa of a certain number of subjects with hepatitis: this case-list included subjects with a tendency to relapse or with a poor chronic course notwithstanding the treatment. Some interpretative hypotheses are set forth.