SummaryThe plasma level of interleukin-1β (IL-1β) was determined in normal individuals, patients with disseminated intravascular coagulation (DIC), patients in the pre-DIC period (within 7 days before the onset of DIC), and non-DIC patients to examine the relationship between DIC and the plasma ILlp level. The plasma IL-1β level was 0-0.085 ng/ml in normal individuals, with little difference being seen according to related age. It was significantly higher in the DIC group (0.19 ± 0.19 ng/ml) than in the pre-DIC group (0.05 ± 0.08 ng/ml) or the non-DIC group (0.09 ± 0.01 ng/ml). The plasma IL-1β level was not markedly elevated in leukemia patients, even in the DIC group, but it was significantly increased in the DIC group of solid cancer patients and was generally elevated in patients with sepsis. It was markedly elevated to 0.39 ± 0.26 ng/ml in patients with organ failure. When mononuclear cells were incubated with lipopolysaccharide, it was found that IL-1β, tumor necrosis factor, and tissue factor (TF) were released into the medium, and there was an increase of TF release from endothelial cells incubated with this medium. These results suggest that the increase in IL-Iβ reflected the activation of monocytes and may be an important factor in DIC and its associated organ failure.