Objective To evaluate the specificity and sensitivity of a Hove]hepatitis C virus NS3 antigen detection immunoassay and the potential application of this assay in clinical diagnosis.Methods Samples from 77 healthy flubjects,173 anti-HCV-positive pailents and 3708 patients infected with other type of hepatitis were tested with the HCV NS3 antigen assay,some HCV NS3 antigen positive samples were validated witll HCV-RNA.neutralization and immunodot assays.Twenty.five sequential samples from 11 HCV NS3 antigen positive patients were subjected to kinetic studv.Results Forty-eight(1.3%)of 3708 antiHCV negative samples were positive for HCV NS3 antigen.Among them,44 of 3030 samples from patients only infected with HBV were HCV NS3 antigen-positive,4 of the 445 samples from patients infected with other type hepatitis were HCV NS,antigen-positive.In addition.42(24.3%)of 173 anti-HCV positive samplea were HCV NS3 antigen-positive and all 77 samples from healthy subjects were negative to HCV NS3 antigen assay.Of 15 HCV NSl antigen-positive samples,9(60%)were HCV-RNA positive.The neutralization and positive percentage of immunodot assay for 23 HCV NS3 antigen-positive sera were 87.0%(20/23)and 69.6%(16/23) respectively.Of the 25 sequential samples from 11 HCV NS3 antigen positive patients,there was a negative correlation between the A values and the duration of test.and there were correlations among their HCV NS3 antigen.HCV.RNA and anti-HCV;In addition,the anti-HCV antibodies of two sera were detected while their A values of HCV NS3 antigen decreased gradually.Conclusion The HCV NS3 antigen detection assay showed perfect specificity and higher sensitivity,it will be useful in routine laboratories test in developing countfies for earlier diagnosis of HCV infection.