It has been tested some diluted HBsAg and anti-HBs positive sera by modified ELISA test. We have found a correlation between HBsAg titer and spectrophotometric reading value and we have shown it in a curve. On the other hand, by neutralization of different dilutions of a RIA anti-HBs positive serum with different dilutions of a HBsAg positive serum we have carried out a checkboard and we have found that the best titer for neutralizing HBsAg is 30 ng/ml. This HBsAg has been called "standard". Using HBsAg "standard" we have tested 50 sera of hemophiliacs and we have found 1 HBsAg positive (2%) and 38 anti-HBs positive patients (76%).
Antibodies, Viral Enzyme-Linked Immunosorbent Assay