The object of this study was to assess the effects of the inflammatory cytokine interleukin beta (IL-1beta) (0. 01?1. 0 ng/ml) on the activity of catalase (CAT), superoxide dismutase (SOD) and the level of glutathione (GSH), all being antioxidant mechanisms, in human peritoneal mesothelial cells (HPMC) in in vitro culture. HPMC were obtained from the omenta of nonuremic donors. The activity of the antioxidant mechanisms was studied on monolayers of HPMC, which were deprived of serum 48 h prior to experiment. The effect of the cytokine was tested in a medium with low serum concentration (0. 1%) or in a medium with 10% fetal calf serum (FCS). Activity of the antioxidant mechanisms was determined by spectrophotometry. The GSH level was decreased in mesothelial cells (MC) after 24 h of exposition to IL-1. However, after 72 h of incubation with IL-1 the GSH level increased in MC in the presence of 10% FCS, p<0.05. The activity of CAT was inhibited after 72 h exposure to IL-1. Interleukin 1 did not affect SOD activity in MC. However, when supplemented with 10% FCS, IL-1 decreased the activity of SOD after 24 and 72 h of incubation. We conclude that the activity of antioxidant mechanisms in MC is decreased by IL-1beta in ways that might increase their vulnerability to the cytotoxic effect of free radicals.