We measured blood concentrations of tumor necrosis factor (TNF), interleukin-1 beta (IL 1-beta), soluble interleukin 2 receptor (s-IL 2r), and interferon alpha (IFN alpha) in 30 patients with disseminated intravascular coagulation (DIC) and compared the results to those of 25 patients without DIC. Plasma levels of TNF, IL 1-beta, and s-IL 2r were higher in patients with DIC than in those without DIC. In one case of acute promyelocytic leukemia, plasma levels of TNF and IL-1 beta increased at the onset of DIC but decreased upon DIC improvement. These findings suggest that activation of the immune system is involved in the development of DIC. However, these concentrations were not markedly increased in patients with leukemia, although blood TNF and s-IL 2 r were markedly elevated in patients with solid cancers. Especially in patients with solid cancers, hyperactivation of the immune system may cause an increase in blood TNF and IL-1 beta and the development of DIC.