“…The reported success rates vary between 70 and 100% [2][3][4][5][6][7][8][9][10], but its mechanism is not yet fully understood [for review, 11]. According to the prevail ing hypothesis it is assumed that 'blocking' antibodies or factors, normally produced by the mother's immune system to protect the fetus against immunological rejection, are absent in patients with RSA, but can be stimulated by transfusion/vaccination with allogeneic leukocytes [1,3,4,[6][7][8][9]11], The formation of lymphocytotoxic and/or noncytotoxic antibodies which inhibit Fc-rosette formation [12,13], immune phagocytosis [13,14] or mixed lymphocyte culture [4,6,8,15] is considered to be an indicator of effective immunization after leukocyte therapy and of a successful outcome of pregnancy [9,10]. Hence, we hy pothesize that intravenous immunoglobulin (IVIG) pro cessed from a large pool of donors should contain pre formed antibodies of similar specificity and therefore might be effective by 'passive immunization' in patients with RSA.…”