Several drugs which react with DNA decrease hepatitis B viral (HBV) DNA polymerase activity in vitro. Because such an alteration of viral replication, if produced in patients with hepatitis B surface antigen (HBsAg)-positive chronic hepatitis, may lead to elimination of viral infection, we conducted a controlled trial of the use of the intercalating agent, quinacrine hydrochloride, in treatment of HBsAg-positive chronic hepatitis. No patient converted from HBsAg positive to negative during the trial and no consistent effect on HBV DNA polymerase activity was noted. Following treatment, elevated transaminase values and alterations of HBV markers were observed in several patients. Fluctuations of transaminase values and HBV markers may reflect alterations in host immunity and viral replication. Quinacrine alone is ineffective in therapy of chronic HBV infection. Additional study with intercalating agents, perhaps in conjunction with other drugs, is suggested.