Fresh frozen plasma (FFP) contains natural anticoagulants, such as antithrombin (AT) and Protein C (Prot-C). We hypothesized that FFP given in addition to heparin, could potentially replace the consumption of endogenous anticoagulants occurring during conditioning and moreover, corrected AT levels could augment heparin's anticoagulant function. This could therefore result in an effective anti-VOD prophylaxis. In this study, we retrospectively analyzed the incidence of hepatic VOD in 403 consecutive bone marrow transplants (BMTs) comparing 2 prophylactic regimens and no prophylaxis. Patients received no prophylaxis (70/403), heparin-only (27/403) or heparin+2FFP daily during conditioning (306/403). VOD was significantly lower in the heparin+FFP group (5.9%) compared to heparin (20%) and no prophylaxis group (15.7%) [p<0.01]. Day 8 AT and Prot-C levels, were lower in the VOD- compared to the non-VOD group (AT: 69+/-26% vs. 89+/-19%, Prot-C:68+/-26% vs. 91+/-29%, respectively, p=0.001). In a multivariate logistic regression, risk factors for developing VOD were: the administration of >2 hepato-nephrotoxic drugs, previous history of hepatitis B or C and number of BMT. Multivariate analysis in a subset of 198 patients (all having recorded AT, Prot-C), demonstrated as VOD-related factors, the low day 8 Prot-C, number of BMT>1 and prior abdominal radiotherapy. Our study implies that FFP during conditioning, in addition to heparin, potentially has an anti-VOD prophylactic effect, presumably by minimizing the drop of natural anticoagulants around day 8. In order to evaluate if there truely is a beneficial effect of heparin+FFP in VOD prophylaxis, we have initiated a prospective randomized trial.