In addition to its established immuno-regulating capacity, the anti-inflammatory cytokine interleukin (IL)-10 exerts direct effects on coagulation. IL-10 down regulates the expression of tissue factor (TF) and thrombin generation (TG). Thus, we hypothesised that IL-10 could enhance the effect of anticoagulants. To evaluate in vitro the potential additive effect of IL-10 on fondaparinux-induced anticoagulation. Human monocytes were purified by elutriation, and were activated by factor Xa (FXa). Real-time RT-PCR and Western blotting were used to evaluate FXa-induced TF synthesis. TG test was used as a functional test to assess TF-dependent monocyte procoagulation, and to evaluate the effects of IL-10 (200 and 500 pg/ml) and fondaparinux (0.0, 0.1, 0.4, 0.7 and 1.2 μg/ml), separately and in combination. We confirmed that FXa induced TF mRNA and protein synthesis by monocyte in a concentration dependent manner. We showed that FXa-activated monocytes triggered TG via TF expression. We reported that IL-10 inhibited TG with a marginal effect seen at 200 pg/ml. Results with fondaparinux showed a concentration-dependent TG inhibition. The combination of IL-10 and fondaparinux effects demonstrated that IL-10: (i) potentiates the inhibitory effect of fondaparinux on TG by 10-30%, and (ii) dramatically modifies fondaparinux IC50 for each TG parameter. IL-10 enhances in vitro the extent of anticoagulation induced by fondaparinux.