IBD is associated with an increased activation of intestinal immune cells, which causes overproduction of proinflammatory cytokines such as IL-1β. IL-1β is implicated in mediating the sustained inflammatory response. IL-1 receptor antagonist (IL-1Ra), the naturally occurring inhibitor of IL-1, has been shown to have beneficial effects in experimental models of colitis. In this study we investigated the hypothesis that an imbalance between IL-1 and IL-1Ra exists in IBD by measuring their secretion by explant cultures of colonic biopsies. Freshly homogenized biopsies from involved tissue in IBD patients exhibited significantly lower IL-1Ra/IL-1β ratios than control and uninvolved IBD mucosal tissue. Using explant cultures, in vitro production of IL-1β and IL-1Ra increased progressively during the 4–18-h culture periods. IL-1β secretion was higher in supernatants from involved Crohn's disease (CD) and ulcerative colitis tissue compared with control tissue, and IL-1β levels increased with severity of inflammation. IL-1Ra secretion was not elevated in involved IBD samples, but significantly higher levels were released when moderate to severely involved tissue samples were compared with non-inflammatory controls. Similar to freshly homogenized tissue, explant studies showed that the IL-1Ra/IL-1β ratios were significantly decreased in involved IBD tissue, but not in uninvolved CD or inflammatory control specimens. These data support the hypothesis of an imbalance between IL-1β and IL-1Ra in IBD.