We investigated plasma levels of cytokines and endotoxin in septic shock to clarify the roles of various cytokines in this type of shock. Endotoxemia was observed in 16 of 22 septic shock patients. Plasma levels of tumor necrosis factor-alpha (TNF-alpha), interleukin 1 beta (IL-1 beta) IL-2, and IL-6 were significantly higher in septic shock than in sepsis without shock. Strong correlations were noted between TNF-alpha and IL-2 levels and between IL-1 beta and IL-6 levels. Patients with high TNF-alpha and IL-2 levels also showed endotoxemia. We defined two types of septic shock from these data, i.e., endotoxin+TNF-alpha + IL-2 shock and IL-beta + IL-6 shock. In the former type, high TNF-alpha and IL-2 levels were present before the onset of shock, and shock itself was associated with endotoxemia. The second type showed simultaneous elevation of IL-1 beta and IL-6 levels at the onset of septic shock, and endotoxin was detected in some of them. These results suggest that endotoxin and extremely high levels of TNF-alpha and IL-2, or the simultaneous elevation of IL-1 beta and IL-6, are related to the onset of septic shock.