Gut microbes are capable of producing most neurotransmitters found in the human brain. Evidence is accumulating to support the view that gut mi-crobes influence central neurochemistry and behavior. Irritable bowel syn-drome is regarded as the prototypic disorder of the brain-gut-microbiota axis that can be responsive to probiotic therapy. Translational studies indi-cate that certain bacteria may have an impact on stress responses and cognitive functioning. Manipulating the gut microbiota with psychobiotics, prebiotics, or even antibiotics offers a novel approach to altering brain func-tion and treating gut-brain axis disorders, such as depression and autism.