Seven patients are described in whom HBsAg persisted for 13 to 98 months after acute viral hepatitis B and then became nondetectable. All patients subsequently developed anti-HBs. During the period of HBs-antigenemia, liver biopsies in five patients showed persistent viral hepatitis. Retrospectively, impending negativity of HBsAg was predictable in five patients by a decrease in HBsAg titer, and in four patients by persistent normalization of serum alanine aminotransferase. Although delayed clearance of HBsAg in patients with chronic hepatitis B virus infection is uncommon, it appears to be predictable.