Chronic delta hepatitis is a severe form of chronic liver disease caused by hepatitis delta virus (HDV) infection superimposed on chronic hepatitis B or the hepatitis B surface antigen (HBsAg) carrier state. Therapy of delta hepatitis is currently unsatisfactory. We have evaluated lamivudine (3-thiacytidine), an oral nucleoside analogue with marked effects against hepatitis B, as therapy in 5 patients with chronic hepatitis D. Five men, ages 38 to 65 years, were treated. All had HBsAg, antibody to HDV, and HDV RNA in serum, as well as persistent elevations in alanine aminotransferase (ALT) levels and liver histology showing severe chronic hepatitis with fibrosis or cirrhosis. Lamivudine was given in a dose of 100 mg orally daily for 12 months. Patients were monitored carefully and tested for HBsAg, HBV-DNA and HDV-RNA levels serially during the year of treatment and for 6 months thereafter. Liver biopsies were performed before therapy and repeated after 1 year. Serum levels of HBV DNA fell rapidly in all 5 patients, becoming undetectable even by polymerase chain reaction (PCR) in 4. However, all 5 patients remained HBsAg-and HDV-RNA-positive, and serum ALT levels and liver histology did not improve. All patients tolerated therapy well. When lamivudine was stopped, HBV-DNA levels returned to pretreatment values without a change in disease activity. Lamivudine is a potent inhibitor of HBV-DNA replication, but does not improve disease activity or lower HDV-RNA levels in patients with chronic delta hepatitis. (HEPATOLOGY 1999;30:546-549.)The hepatitis delta virus (HDV) is a small defective RNA virus that replicates only in the presence of hepatitis B surface antigen (HBsAg). 1,2 Chronic HDV infection often results in severe liver disease that progresses to cirrhosis in as many as 70% of patients. 3 All patients with delta hepatitis have HBsAg in serum, but most lack markers of active hepatitis B virus (HBV) replication such as hepatitis B e antigen (HBeAg) and HBV DNA. Diagnosis is suggested by the finding of anti-HDV in an HBsAg-positive patient and is confirmed by the finding of HDV RNA in serum or HDV antigen in liver. 4 Therapy of chronic delta hepatitis is problematic. Pilot studies suggested that interferon alfa was effective in reducing serum aminotransferase elevations and improving hepatic histology. 5,6 Subsequent randomized, controlled trials showed that interferon was effective in only a proportion of patients and had to be administered in high doses for prolonged periods. [7][8][9][10][11][12] Relapses were common after therapy unless HBsAg was cleared, which occurred uncommonly. 13 Interferon alfa therapy is also expensive, difficult to administer, and often poorly tolerated. Thus, current options for therapy of chronic delta hepatitis are limited.Other antiviral agents have been used in chronic delta hepatitis, but results have been limited. Both ribavirin and levamisole appear ineffective. 14,15 Recently, lamivudine (3-thiacytidine), an oral nucleoside analogue, has been shown to have inhibitory effe...