Background/Aims: The purpose of this study was to investigate the serum HBV DNA status and clinical significance of polymerase chain reaction(PCR) in patients with chronic hepatitis B and asymptomatic HBsAg carriers. Methods: The subjects of this study were 80 patients with chronic hepatitis B(53 HBeAg posiiive patients, 27 HBeAg negative patients), 19 asymptomatic HBsAg carriers(8 HBeAg positive patients, l l HBeAg negative patients). Serum HBV DNA was measured by Dot blot hybrydization with a ' P labeled HBV DNA in all patients studied, and the PCR was used to detect serum HBV DNA in Dot blot negative patients. The PCR was performed with 2 primers in the C gene region of HBV. Amplified sequences were detected with ethidium bromide staining(PCR-EB) and southern blot hybridization(PCR-SBH). Dot blot allowed the detection of 10 ' pg of cloned HBV DNA, while 10 pg and 10' pg were detected by PCR-EB and PCR-SBH, respectively. Results: In the 80 patients with chronic hepatitis, 76patients(95%) were positive for HBV DNA by Dot blot or PCR. All 53 HBeAg positive chronic hepatitis patients had HBV DNA detectable by Dot blot(77.4%) or PCR(18.97c by PCR-EB, 3.7% by PCR-SBH). Out of 27 HBeAg negative patients, 23(85.2%) were positive for HBV DNA by Dot blot (40.8/o) or PCR (29.61o by PCR-EB, 14,8% by PCR-SBH). In the 19 asymptomatic HBsAg carriers, 13(68.4%) were positive for HBV DNA by Dot blot or PCR. All 8 HBeAg positive asymptomatic carriers had sufficient HBV DNA detectable by Dot blot. Out of 1 l HBeAg negative carriers, 5(45.5 7c) were positive for HBV DNA by Dot blot (9.1%) or PCR(36.4%). The positive rate for HBV DNA in patients with chronic hepatitis was significantly higher than that in asymptomatic HBsAg carriers(P=0.002 by Fisher exact test) and there is a significant difference in serum HBV DNA between HBeAg positive and negative asymtomatic HBsAg carriers(P=0.02 by Fisher exact test). Conclusions: These results suggest that minute amount of HBV DNA detected by PCR may have pathogenic relevance in chronic hepatitis B, and PCR may be used as a prognostic factor in asymptomatic HBsAg carriers. (Korean J Gastroenterol 1995;27: 651 - 658)