The success of a clinical trial is judged by achieving statistical and clinical significance on the primary endpoint. This is particularly relevant in those trials that are initiated to achieve regulatory approval of a new therapeutic agent. Selection of an endpoint for which statistical significance will be too difficult to achieve can result in clinical trial data that fails to meet regulatory requirements for product approval. Over the past decade, significant progress has been made in development and refinement of the study design for evaluating new therapeutic agents targeted for the treatment of irritable bowel syndrome. One aspect of trial design that has been advanced is recognition of the endpoint of 'Adequate Relief.' Adequate relief has been used as a primary endpoint in treatment trials with alosetron, cilansetron and dextofisopam. With each of these agents, statistically significant benefit was seen when compared to placebo. As an endpoint, adequate relief is responsive, reproducible and moves in the same direction as other meaningful measures, and, therefore, displays properties of a validated endpoint. Adequate relief should be considered an acceptable primary endpoint by regulatory agencies for use in clinical trials of novel therapeutic agents for irritable bowel syndrome.