AIM:TT virus (TTV) is a newly described DNA virus relatedto postransfusion hepatitis that produces persistent viremiain the absence of clinical manifestations.PEG-IFN plusribavirin have been useful in the treatment of chronic hepatitisC infection.This study investigated the responses of TT virus(TTV) and hepatitis C virus (HCV) to PEG-IFN plus ribavirintherapy.METHODS:Fifteen patients infected with HCV were treatedwith PEG-IFN(0.5 μg/body weight/week) and ribavirin(1000 mg-1 200 mg/daily) for 48 weeks,Blood samples weredrawn at the beginning and the end of the therapy.SerumTTV DNA and HCV RNA were quantified by real time PCR.RESULTS:At the beginning of treatment,TTV infection wasdetected in 10/15 (66.6%) of HCV-infected patients.Lossof serum TTV DNA at the end of therapy occurred in 6/10(60%) patients.Out of these 6 patients,4 (67%) becamepositive for TTV DNA after 6 months of therapy.RegardingHCV viremia,11/15 (73%) patients were negative for serumHCV RNA after 48 weeks of therapy,7/11 (64%) of thesecases also became negative for TTV DNA following thecombined treatment.In the 3/4 (75%) patients who werepositive for HCV RNA at the end of therapy,TTV DNA wasdetected as well.Sustained HCV response at 6 months aftertreatment was 53% (8/15).CONCLUSION:No TTV sustained response can be achievedin any patient after PEG-IFN plus ribavirin administration. AIM: TT virus (TTV) is a newly described DNA virus relatedto postransfusion hepatitis that produces persistent viremiain the absence of clinical manifestations. PEG-IFN plus ribavirin have been useful in the treatment of chronic hepatitis C infection. This study investigated the responses of TT virus ( TTV and hepatitis C virus (HCV) to PEG-IFN plus ribavirin therapy. METHODS: Fifteen patients infected with HCV were treated with PEG-IFN (0.5 μg / body weight / week) and ribavirin (1000 mg- 1 200 mg / 48 weeks, Blood samples weredrawn at the beginning and the end of the therapy. Serum TTV DNA and HCV RNA were quantified by real time PCR .RESULTS: At the beginning of treatment, TTV infection was detected in 10/15 (66.6%) of HCV- infected patients. Loss of serum TTV DNA at the end of the 9th (60%) patients. Out of these 6 patients, 4 (67%) becamepositive for TTV DNA after 6 months of therapy. RegulatoryHCV viremia, 11/15 (73%) patients were negative for serum HCV RNA after 48 weeks of therapy, 7 / 11 (64%) of thesecases also became negative for TTV DNA following thecombined treatment.In the 3/4 (75%) patients who werepositive for HCV RNA at the end of therapy, TTV DNA wasdetected as well.Sustained HCV response at 6 months aftertreatment was 53% (8/15). CONCLUSION: No TTV sustained response can be achieved in any patient after PEG-IFN plus ribavirin administration.