Chronic hepatitis B virus (HBV) infection is a serious problem because of its world wide distribution and possible adverse chronic sequalae such as cirrhosis and hepatocellular carcinoma. Over the past 20 years, many antiviral or immunomodulatory agents, or both, have been used in patients with chronic HBV infection. Among immunomodulatory agents, levamisole, BCG, picibanil and interleukin-2 have been shown to be ineffective. Corticosteroid therapy is also ineffective and can cause deleterious effects in chronic HBV infection. Thymosin-alpha 1 therapy is currently in phase III clinical trial. Among antiviral agents, acyclovir, dideoxynucleosides, suramin, zidovudine and ganciclovir have been shown to be ineffective and have intolerable side effects. While adenine arabinoside (Ara-A) and its monophosphate derivative (Ara-AMP) are effective agents if the treatment course is long enough, they have been withdrawn from investigative use because of their substantial neuromuscular toxicity. Interferon-alpha may directly inhibit HBV replication and enhance hepatocyte HLA class I antigen expression with subsequent increase of T-cell mediated cytotoxicity. Randomized, controlled clinical trials have shown that 25% to 50% of adult patients with elevated alanine transaminase (ALT) levels lost HBeAg and HBV-DNA when treated with IFN-alpha at a dose of 5MU daily or 10 MU three times a week for 3 to 6 months. In view of the fact that the response rate is far from satisfactory, particularly in Asian patients, combination therapies including interferon alpha with Ara-AMP, acyclovir, didoxynucleoside or interferon-gamma have been studied. Most forms of combination therapy have been shown to be of limited effect.(ABSTRACT TRUNCATED AT 250 WORDS)