A change in gut microbiome reinforces the etiology of inflammatory bowel disease (IBD). For this reason, administration of agents (such as antibiotics) that can potentially alter the balance of gut microbes could potentially affect the course of IBD. Antibiotics can, therefore, be used to rid the gut of harmful microbes. Probiotics are useful to introduce beneficial microbes. In addition, prebiotics may provide a metabolic substrate that enhances the growth of these beneficial microbes. In this presentation, Dr Bernstein reviews data from studies that have assessed the use of antibiotics, probiotics and prebiotics in patients with IBD. In addition to presenting the efficacy data, he also discusses the risks associated with these agents. The timing of antibiotic administration and dietary factors also influences gut microbiome, which in turn may either predispose or prevent IBD.