Intravenous immunoglobulin (IVIg) therapy for antibody-mediated rejection (AMR) is increasing and is associated with a small but significant incidence of thrombosis. We determined thrombosis rates in patients treated with high-dose IVIg for AMR before and after alteration of an infusion protocol. The newer protocol introduced routine administration of aspirin 300 mg, enoxaparin 1 mg/kg, intravenous hydration and a maximum infusion rate of 100 mg/kg per hour (previously 200 mg/kg per hour). Nine thromboses in 275 infusions occurred before the protocol alteration (event rate 3.3 ). Two were arterial thromboses including an acute myocardial infarct and a renal transplant artery thrombosis, which resulted in infarction of 2/3 of the graft. Seven venous thromboses occurred, six in arteriovenous fistulae and one case with bilateral above knee deep venous thromboses. Significant associations with thromboses were seen with higher IVIg dose and male sex. In the 6 months since the introduction of the new infusion protocol, 74 infusions have been administered with no thrombotic events. There have been no significant bleeding or fluid overload side-effects. Infusion times, however, have been doubled. A slower rate of infusion combined with antiplatelet and anticoagulation has thus far eliminated the small but significant IVIg-related thrombosis rate previously observed in our patients treated for AMR without resulting in significant side-effects. Further study is now required to define which elements of this protocol are essential.