Inflammation in Behcet's disease is thought to be mediated by cytokines derived from T-helper type 1 (Th1) lymphocytes. In this study, we tried to determine serum interleukin (IL)-18 and tumour necrosis factor (TNF)-alpha levels of patients with Behcet's disease. Twenty-seven patients with active Behcet's disease, and 20 healthy control subjects were included in this study. Differences between mean serum IL-18 and TNF-alpha level of patients with Behcet's disease were significantly increased when compared with the control group. A significant correlation was found between serum IL-18 and TNF-alpha levels of Behcet patients (r(s) = 0.627, P < 0.0001). IL-18 and TNF-alpha levels may be related to disease pathogenesis. Increased levels of IL-18 also support Th1 predominance in Behcet's disease.