AIM: The aim of this study was to evaluate the association between ulcerative colitis activity and plasma or mucosal concentrations of interleukin (IL)-18.METHODS:Il-18 concentrations were measured in plasma and mucosal samples from 15 patients with active ulcerative colitis (UC).RESULTS: The mean plasma concentration of IL-18 measured in all patients (422±88 pg/mL) doubled the mean value in healthy controls (206±32 pg/mL); however,the difference was not statistically significant. Plasma IL-18 levels revealed a significant positive correlation with scored endoscopic degree of mucosal injury, disease activity index, clinical activity index and C-reactive protein concentration. The mean concentration of plasma IL-18 was significantly higher in patients with severe ulcerative colitis (535±115 pg/mL) than in patients with mild ulcerative colitis (195±41 pg/mL), and in healthy controls.Although the mucosal mean IL-18 concentration in severe ulcerative colitis (2 523±618 pg/mg protein) doubled values observed in mild one (1 347±308 pg/mg protein), there was no statistically significant difference.CONCLUSION: Plasma IL-18 can be considered as a surrogate marker helpful in evaluation of ulcerative colitis activity.