AIM:To investigate the serum positive percentage of TTvirus(TTV)in patients with chronic hepatitis B or C and theresponse of the coinfected TTV to interferon(IFN)duringIFN therapy for chronic hepatitis B and C.METHODS:We retrospectively studied the serum samples of70 patients with chronic hepatitis who had received IFN-alfatherapy from January 1997 to June 2000,which included 40cases of hepatitis B and 30 hepatitis C.All the patients hadbeen followed up for at least 6 months after the end of IFNtherapy.The serum TTV DNA was detected using thepolymerase chain reaction(PCR)before and every monthduring the course of IFN treatment.RESULTS:TTV infection was detected in 15 %(6/40)of thechronic hepatitis B group and 30 %(9/30)of the chronichepatitis C group.Loss of serum TTV DNA during IFNtherapy occurred in 3 of 6 patients(50 %)and 6 of 9(67 %)of hepatitis B and C groups,respectively.Seronegativity ofTTV was found all during the first month of IFN therapy inthe 9 patients.There was no correlation between theseroconversion of TTV and the biochemical changes of thepatients.CONCLUSION:TTV is not infrequently coinfected in patientswith chronic hepatitis B and C in Taiwan,and more thanhalf of the TTV infections are IFN-sensitive.However,theloss of serum Trv DNA does not affect the clinical course ofthe patients with chronic hepatitis B or C. AIM: To investigate the serum percentage percentage of TTvirus (TTV) in patients with chronic hepatitis B or C and the response of the coinfected TTV to interferon (IFN) during IFN therapy for chronic hepatitis B and C. METHODS: We retrospectively studied the serum samples of 70 patients with chronic hepatitis who had received IFN-alfatherapy from January 1997 to June 2000, which included 40cases of hepatitis B and 30 hepatitis C. All patients who hadbeenfol up for at least 6 months after the end of IFNtherapy. The serum TTV DNA was detected using the polymerase chain reaction (PCR) before and every month during the course of IFN treatment. RESULTS: TTV infection was detected in 15% (6/40) of the chronic hepatitis B group and 30% (9/30) of the chronic hepatitis C group . Loss of serum TTV DNA during IFN treatment of 3 of 6 patients (50%) and 6 of 9 (67%) of hepatitis B and C groups, respectively. Sero-conjugation of TVS was found all during the first month of IFN therapy . Was was no correl ation between the seroconversion of TTV and the biochemical changes of the patients. CONCLUSION: TTV is not infrequently coinfected in patients with chronic hepatitis B and C in Taiwan, and more thanhalf of the TTV infections are IFN-sensitive. Still, theloss of serum Trv DNA does not affect the clinical course of the patients with chronic hepatitis B or C