The plasma level of tumor necrosis factor (TNF) was determined in 20 normal individuals, 52 patients with disseminated intravascular coagulation (DIC), 22 pre-DIC patients, and 39 non-DIC patients. TNF was not detected in the normal subjects, and the level was very low in non-DIC patients. However, the TNF level was significantly elevated in DIC patients, and it was moderately increased in pre-DIC patients shortly before the onset of DIC. This increase in circulating TNF may be associated with DIC. TNF was higher in DIC associated with solid cancer than in DIC associated with leukemia or sepsis. The increase in plasma TNF level was mildly correlated with DIC score, and it was significantly increased in patients with poor prognosis. However, the plasma TNF level in DIC patients with organ failure was not significantly different from those without organ failure. We conclude that the increase in circulating TNF reflects the pathogenic factors in DIC rather than being a consequence of organ failure due to DIC.