Since the presence of DNA-polymerase has been reported by Hirschman et al, In concentrated preparations containing Au antigen, the activity of DNA-polymerase has been used as the index of degree of the viral replication and as the ost sensitive marker for the effects of antiviral therapy. The activity of DNA-polymerase was measured through radiological assay in 80 patients with HBsAg positive chroriic HBV infection(57 patients with chronicactive hepatitis, 12 with chronic persistent hepatitis and 11 with liver cirrhosis) and serially checked for aboutone year in 37 patients with HAsAg positive chronic active hepatitis, whoreceived 4 weeks Ara-AMP therapy. The following results were obtained; 1) The mean DNA-polymerase activity of the HBeAg positive chronic hepatitis patients was significantly higher than that of the HBeAg negative patients(p<0. 05), but differences of the SGOT and SGPT levels between the both groups were not significant(p>0.05). 2) The differences of mean DNA-polymerase activity among the chronic active hepatitis, chronic persistent hepatitis and liver cirrhosis were not significant(p>0.05). 3) During the 4 weeks of Ara-AMP therapy, the mean levels of DNA-polymeraee activity, SGOT fell dramatically. 10 of 16 patients who could follow up for over 24 weeks maintained DNA-polymerase activity normal. However, remaining g relapsed. From 1 to g months after therapy, 7 of 16 patients became HBeAg negative, while only one of 6 controls became HBeAg negative, 4) Side effects of Ara-AMP such as anorexia (21.6%), nausea(16.2%), general weakness(16.2%), paresthesia(2.7%), granulocytopenia(2.7%), and thrombocytopenia(2.7%) were observed. In conclusion, the measurement of DNA-polymerase activity will be helpful in evaluation of infectivity of chronic viral hepatitis and effect of antiviral therapy. More work is needed to determine whether the use of Ara-AMP in more pro- longed or repeated courses or both, and application earlier in the course of the illness might be more effect in the eradication of virus and in stopping progression of chronic liver disease. Alternatively, Ara-AMP may be more effective when combined with antiviral agents, and controlled studies to evaluate various combination regimens are required.