BACKGROUND: According to the development of molecular biology, many methods such as polymerase chain reaction (PCR), DNA-RNA hybridization, and branched DNA (bDNA) have been introduced to diagnose and monitor the hepatitis B infection. In our hospital, we have measured serum HBV DNA using the bDNA signal amplification assay to monitor the HBV infected patients treated with lamivudine since 1999. But sometimes we've had difficulties in interpretating the results of the samples showing weak positivity (2.5 - 10 pg/mL) because they were converted to negative when retested. In this study, we compared the results of bDNA with serologic markers and performed PCR in samples showing discrepancy between two results. Also, we investigated the samples showing weak positivity in bDNA. METHODS: We analyzed the results from 495 patients referred for the evaluation of HBV-DNA and serologic markers, over a period from November 1999 to June 2001. HBV-DNA quantitation was performed by VERSANT(TM) HBV DNA Assay (bDNA) (Bayer Corp., NY, USA) and serologic markers by AxSYM(R) system (ABBOTT, IL, USA). In samples showing discrepancy between bDNA and serologic markers, we performed HBV-PCR. Also, we randomly selected 10 sera showing weak positivity in bDNA and performed bDNA retest and PCR with them. RESULTS: The bDNA and HBsAg were tested simultaneously in 293 among 495 patients and their concordant rates were 60%. The number of patients showing discrepancy between two tests were as followed: bDNA(+)/HBsAg(-), 5 patients (1.7%); bDNA(-)/HBsAg(+), 112 (38.2%). Seven patients showed both bDNA and anti-HBs positivity, and 5 of them were also HBsAg positive. The concordant rate between HBeAg and bDNA were 75.3%, and the number of patients showing discrepancy were as followed: bDNA(+)/HBeAg(-), 79 patients (18.5%); bDNA(-)/HBeAg(+), 27 (6.3%). Among 10 sera showing weak positivity in bDNA, 6 showed negative results in retest and 4 of them were also negative in PCR. CONCLUSIONS: It was thought that careful examination of the previous data and clinical findings is needed in patients showing weak positivity (2.5 - 10 pg/mL) in bDNA. Also, if necessary, further study such as PCR is needed to report the patient's data more accurately.