Antiphospholipid syndrome (APLS) is characterized by anti-cardiolipin antibodies (ACA) and/or lupus anticoagulant, recurrent thromboembolic phenomena, thrombocytopenia, and recurrent fetal loss. Recently, we reported on the induction of experimental APLS by passive transfer of ACA to naive mice. In the current study we examined the effect of intravenous γ-globulins (IVGG) on the obstetric complication of experimental APLS. After showing the binding of IVGG to mouse and human ACA (e.g., the existence of natural anti-idiotypic autoantibodies to ACA) we infused 36 μg of IVGG to the tail vein of mice in which experimental APLS was induced by passive transfer of monoclonal mouse ACA (CAR). Mice treated with IVGG had significantly less fetal resorptions when mated, in comparison to untreated mice (5-13 ± 6% vs 25 ± 17%). The best results were achieved when IVGG was given 2 days after induction of the disease (on Day 6 of pregnancy). It seems that IVGG may be employed as a good adjunct to any therapy of APLS.