This study was aimed to develop a more accurate method for the detection of HBV(Hepatitis B Virus) infection in the donated sera at the Kyounggi Do Red Cross Blood Center. The samples were collected from February 1998 to August 1998. The sera were devided into 5 groups(A, B, C, D, and E) according to OD(Optical Density)value of EIA(Enzyme Immunoassay). EIA,RIA(Radio Immunoassay) and PCR(Polymerase Chain Reaction)were performed for these samples to compare the results. Among 10 samples of group A(cut off : 0.050~0.073). EIA for HBsAg was negative for the whole sample, but the result of RIA was found to be negative for 9 sample with one positive. The results of neutralization test were the same in EIA and RIA. The sera of group C which were equivocal by EIA were found to be negative by RIA. The group D(OD value : 0.500~l.000) showed 9 positive sera by EIA of HBsAg, but only one positive by RIA of HBsAg. For group E. the result of EIA was in perfect accordance with that of RIA except one serum. Late confirmation of this serum proved that the result of the first EIA was false positive. Dilution experiments showed that the sensitivity of PCR was 105~6 time higher than EIA. When the result of PCR-amplified HEV DNA detection was compared with those of EIA and RIA, the presence of HBV was confirmed even in group A. which group was judged safe by EIA and RIA. This result suggests that a more accurate method like PCR-amplification of HBV DNA should be developed for the safety of public health.