The in vivo relationship between the immune and the coagulation systems is a well documented fact. In a number of pathological conditions, thrombosis is not understood isolately, but in the context of inflammation and immunity. The mediators in these complex multidirectional interactions are the cytokines, a group of soluble peptides which act on surface cellular receptors, with immunoregulatory properties. These molecules influence negatively the physiological antithrombogenic situation by two different mechanisms. They are involved in processes which disrupt the endothelial integrity, and at the same time, they are capable of activating the endothelium in a prothrombotic manner, by stimulating procoagulant activities and by inhibiting different anticoagulants.