BACKGROUND Hepatitis B surface antigen (HBsAg) is one of the most important serological markers used to diagnose hepatitis B virus (HBV) infection. Automated immunoassays have been developed, meeting the current clinical requirement of HBsAg assays over the years. This study was performed to determine the degree of agreements between 3 kinds of HBsAg assay systems. METHODS Serum samples from 425 patients were assayed by the HBsAg assay systems of Elecsys (Roche Diagnostics, Germany), ADVIA Centaur (Bayer Diagnostics, USA), and AxSYM (Abbott Laboratories, USA). RESULTS The concordance rates among the 3 assays were 100%. A total of 249 (58.6%) specimens were positive, and their index values showed a weak correlation between the 3 assays; nevertheless, positive specimens with low levels (<10) of index values in one system also presented low values in other systems, and all of them were confirmed by neutralization assays. CONCLUSIONS The 3 automated HBsAg assay systems presented a high level of concordance.