Abstract
Spherical 20 nm diam. particles of hepatitis B surface antigen (HBsAg), purified from some sera positive for hepatitis B e-antigen (HBeAg), are associated with antigenic determinants reacting with antibodies frequently present in sera containing anti-HBe. Treatment of HBsAg with the detergent Sarcosyl increased the exposure of these determinants which could be differentiated from HBeAg on the basis of immunological specificity and sensitivity to reduction and alkylation. The presence of these determinants appeared to be restricted to a subpopulation of HBsAg associated with IgG and albumin.