Probiotics and prebiotics are the sort of therapy that most patients with inflammatory bowel disease (IBD) wish for. They are without significant side effects, except possibly an increase in gas with prebiotics, and so far, appear to be entirely safe. However, are they effective? More than a dozen studies using probiotics in IBD have now been reported, and there is dear benefit in pouchitis and possibly also in Crohn's, although there are so many clinical types of this condition that a clear indication has yet to emerge. For ulcerative colitis (UC) more studies are needed. The use of prebiotics in IBD is only just starting, although significant effects on both the luminal and mucosa-associated flora have been demonstrated in healthy subjects. Antibiotics offer more certain hope in IBD treatment, although with a much greater risk of unwanted effects. Their efficacy in clinical studies varies, with Crohn's disease and pouchitis reporting more benefit than ulcerative colitis. However, the ideal combination of antibiotics, and rationale for their use has not been determined.