AIM:To test whether in vitro incubation of peripheral bloodmononuclear cells (PBMC) with interferon (IFN) couldefficiently decrease hepatitis C virus-RNA (HCV-RNA) amountand to analyze whether this effect was associated with clinicalresponse to IFN.METHODS:Twenty-seven patients with histologically provenchronic hepatitis C were given intravenous administrationof 6 million units (MU) IFN-β daily for 6 weeks followed bythree times weekly for 20 weeks.PBMC collected beforeIFN therapy were incubated with IFN-β and HCV-RNA inPMBC was semi-quantitatively determined.RESULTS:Twenty-five patients completed IFN therapy.Eight patients (32%) had sustained loss of serum HCV-RNAwith normal serum ALT levels after IFN therapy (completeresponders).HCV-RNA in PBMC was detected in all patients,whereas it was not detected in PBMC from healthy subjects.In vitro administration of IFN-β decreased the amount ofHCV-RNA in PMBC in 18 patients (72%).Eight of thesepatients obtained complete response.On the other hand,none of the patients whose HCV-RNA in PBMC did notdecrease by IFN-β was complete responders.Multiple logisticregression analysis revealed that the decrease of HCV-RNAamount in PBMC by IFN-β was the only independent predictorfor complete response (P<0.05).CONCLUSION:The effect of in vitro IFN-β on HCV in PBMCreflects clinical response and would be taken into accountas a predictive marker of IFN therapy for chronic hepatitis C. AIM: To test whether in vitro incubation of peripheral blood mononuclear cells (PBMC) with interferon (IFN) couldefficiently reduced hepatitis C virus-RNA (HCV-RNA) amount and to analyze whether this effect was associated with clinical response to IFN.METHODS: Twenty-seven patients with histologically proven chronic hepatitis C were given intravenous administration of 6 million units (MU) IFN-β daily for 6 weeks followed bythree times weekly for 20 weeks. PBMC collected beforeIFN therapy were incubated with IFN-β and HCV-RNA inPMBC was semi-quantitatively determined.RESULTS: Twenty-five patients completed IFN therapy. Eight patients (32%) had sustained loss of serum HCV-RNA with normal serum ALT levels after IFN therapy (completeresponders). HCV-RNA in PBMC was detected in all patients, was not detected in PBMC from healthy subjects. In vitro administration of IFN-β decreased the amount of HCV-RNA in PMBC in 18 patients (72%). Eight of thesepatients obtained complete response.On the oth er hand, none of the patients whose HCV-RNA in PBMC did not create by the IFN-beta was complete responders. Multiple logistic regression analysis revealed that the decrease of HCV-RNAamount in PBMC by IFN-beta was the only independent predictorfor complete response (P < 0.05). CONCLUSION: The effect of in vitro IFN-beta on HCV in PBMC reflections clinical response and would be taken into account as a predictive marker of IFN therapy for chronic hepatitis C.