Human B-lymphoblastoid cell lines producing specific anti-D antibodies against Rh0(D) antigen have been established by EBV-transformation. The strong influence of the donor's immune status (serum titer of anti-D antibodies, intravenous booster injection prior to bleeding) is shown. The cell lines cloned by limiting dilution continuously produce anti-D antibodies in culture for 7 months or longer which is sufficient to support large-scale production of anti-D antibodies based on the cultivation of cryopreserved cells. Anti-D IgGl monoclonal antibodies obtained react with Rh-positive and Du cells but not with Rh-negative cells in serological tests. These human monoclonal antibodies could be useful in the prevention of Rh hemolytic disease of newborns.