In this study, were compared two methods used in case-finding of the australian antigen (Ag. HBs) : the electro-immunodiffusion technique (E.I.D.) and the passive reverse hemagglutination tests. All the tests were carried out on couple of sera obtained from mothers and her newborns, giving on the whole 717 sera. The results we obtained led us to maintain the E.I.D. for the biological diagnosis of B virus hepatitis. The passive reverse hemagglutination test has been kept back for the titration of the Ag. HBs in the sera found positive by E.I.D. With regard to the vertical transmission (mother-newborn) of Ag. HBs, we could not draw any good conclusion.