ABSTRACT In this S10 application, funds are requested to purchase a new system for mouse metabolic phenotyping to serve the many researchers interested in metabolism at Washington University in St. Louis. We are seeking to acquire a Phenomaster Next Generation (NG) mouse metabolism phenotyping system with modules for measuring physical activity, food intake, oxygen consumption, carbon dioxide production, and other metabolic parameters concurrently in sixteen individual cages. Moreover, this system will also provide two motorized treadmills for measuring these parameters during exercise challenges. Lastly, the new system will be enclosed in an environmental chamber to control light cycles, prevent environmental stressor exposure, and control the temperature in a range from 3-30ºC. We have identified more than a dozen Washington University faculty members who are NIH funded and will be major users for this system. In addition, several minor users were also identified. These faculty members are appointed in a variety of departments across Washington University, which illustrates the cross-disciplinary interest in metabolism at the institution and also emphasizes the collaborative nature of our university. The PhenoMaster NG system would be housed in the Animal Models Research Core, which serves both the Diabetes Research Center and Nutrition Obesity Research Center at Washington University. Currently, this core uses a PhenoMaster system that is several years old, employs antiquated technology, comprises only eight cages, and currently is reserved several months in advance with users waiting to gain access. The new system would alleviate much of this wait time and with the technologic advances it provides, would improve rigor and reproducibility of the experiments conducted in this system. The additional modules (treadmills and 13CO2 sensors) included in the system will also provide new experimental opportunities and endpoints for rigorous characterization of metabolic phenotypes. Successful acquisition of the PhenoMaster NG will enhance throughput, accuracy, and precision of an existing metabolic phenotyping facility that serves multiple NIH-funded investigators across campus.