The lack of an effective drug against chronic type B virus infection has led to trials of variety of antiviral drugs. Among these drugs interferon has shown more encouraging results. In all studies, greater HBeAg to anti-HBe seroconversion rates occurred in treated patients than in control. The reason for the use of interferon in this disease is the effectiveness as an antiviral activity. More recently its activity has heen extended as an immunomodulating drug in the immune response. The purpose of this study was to elucidate the effect of human fibroblast interferon (β-interferon) in Korean HBsAg positive chronic active hepatitis. We has conducted therapeutic trial with total l02 X1000000 IU of beta-interferon for 28 days in fifteen cases with needle aspiration biopsy proven chronic activc heaptitis. 1) Six patients (40.0%) lost HBeAg in the serum and four of these patients (26.7%) were seroconverted to anti-HBe after β-interferon therapy. And two patients expressed anti-HBe without loss of HBeAg. However, none of the patients lost HBsAg during the study peroid. 2) The serun ALT began to increased significantly (p<0.05) from the 7th day of interferon therapy and reached its maxinauin level on 10th day of therapy, and then continued to decrease to the level below the pretreatment level in 2nd week after treatment of interferon. 3) Pre-tretament ALT showed higher levels in group of changed viral rnarkers (n=6) than in unchanged (n=8), but there was no statistical significance. 4) Peripheral blood leukocytes and granulocytes showed significant reduction in number from the 3rd day of interferon treatment (p<0.05), and recovered within one week after withdrawal, 5) There was no significant changes in serum protein, bilirubin and prothrombin time. 6) All the treated patients experienced an initial flu-like illness consisting of fever, chills, malaise, myalgia, anorexia, headache and dizzeness. Tachyphylaxis developed gradually during the treatment. The above results suggest that β-interferon therapy may be effective and safe in the treatment of patients ivith tvpe B chronic activc hepatitis.