Although the causes of inflammatory bowel disease (IBD) remain incompletely understood, increasing evidence implicates intestinal microflora in the pathogenesis of these disorders. Alteration of intestinal flora therefore may offer a plausible therapeutic approach. Although recent data support a potential therapeutic role for probiotics and prebiotics in patients with IBD, such treatments need to be further assessed by large, double-blind controlled trials. A better understanding of the intestinal microflora and the mechanisms of their action may help us to develop more effective treatment for IBD.