The yearly incidence of viral hepatitis among Peace Corps volunteers who were given semiannual injections of 0.05 ml of immune serum globulin (ISG) per pound of body weight was found to average 0.97 cases per 100 person-years of residence abroad. This rate is considerably lower than those rates reported for volunteers when less extensive ISG programs were in use and for missionaries receiving no ISG. Of 93 icteric cases evaluated in detail, 16 occurred within two weeks after ISG injection; 31 occurred from 16 to 26 weeks; 29 occurred after 26 weeks; and only 17 occurred from 3 to 16 weeks after ISG injection. Cases of hepatitis occurred throughout the two-year period abroad. The data suggest that administration of ISG in this dosage every four months for the entire period abroad would further reduce the incidence of hepatitis.