Plasma Interleukin-6 (IL-6) level was measured in 60 patients with disseminated intravascular coagulation (DIC). Plasma IL-6 level was high in patients with DIC, and was particularly high in patients with multiple organ failure (MOF) or poor prognosis. Plasma IL-6 level correlated positively with C-reactive protein in patients without DIC, but not in those with DIC. The increased plasma IL-6 level observed in DIC patients suggests that activation of the immune system is involved in the progression of DIC and in the pathology of organ failure.