In a study of 63 allogeneic and autologous bone marrow transplants, patients were randomized to receive the IgM and IgA enriched intravenous immunoglobulin (IVIG) preparation (Pentaglobin). Pentaglobin has been postulated to have anti-endotoxin properties and one of the aims of the study was to measure endotoxin levels in these patients together with the clinical sequelae of infection. The anti-endotoxin effects of Pentaglobin were found to reside in the IgM fraction. Those patients who received Pentaglobin were significantly protected from dying from infection in the first 100 days after the transplant, although it was not actually possible to document bacterial infections as the cause of death in the control patients. Peak endotoxin levels were significantly reduced (p = 0.02) in those patients receiving Pentaglobin. Liver damage as assessed by liver enzyme abnormalities correlated significantly with the presence of endotoxaemia greater than 25 pg/ml and up to 70% of pyrexial episodes were associated with endotoxaemia. Our results suggest that Pentaglobin is useful in reducing hepatic toxicity and this may be related to a reduction in endotoxaemia.