Interleukin (IL)-32 is a recently described proinflammatory cytokine, characterized by induction of nuclear factor (NF)-kappaB activation. We studied IL-32alpha expression in the inflamed mucosa of inflammatory bowel disease (IBD). We also investigated mechanisms regulating IL-32alpha expression. Tissue samples were obtained endoscopically or surgically from patients with ulcerative colitis (UC) (n = 10), Crohn's disease (CD) (n = 10), ischaemic colitis (n = 4) and normal colorectal tissues (n = 10). IL-32alpha expression was evaluated by standard immunohistochemical procedure. IL-32 mRNA expression was analysed by Northern blot. IL-32alpha was expressed weakly by colonic epithelial cells from normal individuals and subjects with ischaemic colitis. In the inflamed mucosa of IBD patients, epithelial IL-32alpha expression was increased markedly. In UC and CD patients, IL-32alpha expression was enhanced in affected mucosa compared to non-affected mucosa. In intestinal epithelial cell lines, expression of IL-32alpha mRNA and protein was enhanced by IL-1beta, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha. A combination of TNF-alpha plus IFN-gamma exerted synergistic effects. IL-32alpha induction by IL-1beta and/or TNF-alpha was mediated by NF-kappaB activation. Epithelial IL-32alpha expression was increased in IBD patients, and in CD patients in particular. IL-32alpha might be involved in the pathophysiology of IBD as a proinflammatory cytokine and a mediator of innate immune response.