AbstractThe binding activity of polymerized human serum albumin was determined in 202 HBsAg carriers. The presence of polymerized human serum albumin receptor sites was tested by hemagglutination and differentiated from antihuman albumin antibodies by immunofluorescence, isolation of IgG and IgM fractions and testing of HBsAg anti‐HBs immune complexes. A granular pattern with anti‐HBs was specific for polymerized human serum albumin receptor sites as demonstrated with purified HBsAg. In addition, a linear pattern with fluoresceinated antihuman immunoglobulins might suggest the presence ofantihuman albumin antibodies (which was generally due to an IgG antibody). However, a granular pattern with fluoresceinated antihuman immunoglobulins may indicate the presence of HBsAg anti‐HBs immune complexes. A weak linear pattern was also observed simultaneously in these cases, probably due to IgM antihuman albumin antibodies or an antipolymerized human serum albumin receptor site antibody.Of 202 HBsAg‐positive patients, 71 showed polymerized human serum albumin receptor sites activity. The highest percentage of polymerized human serum albumin receptor sites was found among patients showing HBeAg and hepatitis B virus DNA polymerase positivity (96%), followed by HBeAg positivity and hepatitis B virus DNA polymerase negativity (48%), and anti‐HBe positivity and hepatitis B virus DNA polymerase negativity (17%). In addition, a significant correlation between polymerized human serum albumin titers and hepatitis B virus DNA polymerase was found (r = 0.573, p<0.01). However, at a similar HBeAg titer, patients who were positive for hepatitis B virus DNA polymerase had a higher polymerized human serum albumin receptor sites titer than those who were negative for hepatitis B virus DNA polymerase.The presence of a granular pattern with anti‐HBs or fluoresceinated antihuman immunoglobulins means a positivity to polymerized human serum albumin receptor sites or the presence of HBsAg anti‐HBs immune complexes, respectively. Furthermore, polymerized human serum albumin receptor sites titers correlate with hepatitis B virus DNA polymerase concentrations and may serve as indicators of vira