IL-18 levels in the blood of 13 sepsis patients were assessed. The IL-18 values were significantly correlated with their Acute Physiology and Chronic Health Evaluation (APACHE) II scores, and they were a good reflection of the severity of the disease. There was also a strong correlation between the IL-18 values and the patients' inflammatory cytokine levels. The results suggested strong involvement of IL-18 in the pathogenesis of sepsis.