This document provides methods and materials involved in assessing and/or treating a mammal having a functional gastrointestinal disorder (FGID) such as irritable bowel syndrome (IBS). For example, methods and materials provided herein can be used for determining if a mammal having a FGID is likely to respond to a particular FGID treatment. This document also provides methods and materials for treating a mammal having a FGID.