PROJECT ABSTRACT Children’s Hospital Los Angeles (CHLA) requests funds to purchase a Leica STELLARIS 5 confocal microscope to be housed in the established Cellular Imaging Core Facility of The Saban Research Institute (TSRI), one of the few freestanding research centers in the U.S. where scientific inquiry is combined with clinical care and is devoted exclusively to children. Our investigators rely on confocal microscopy to probe the cellular and molecular mechanisms underlying development and disease, spanning organ systems, in diverse pediatric populations. There is a strong rationale for the request. First, there are two Zeiss 7-series confocal microscopes (LSM 710 and 700) in the Cellular Imaging Core that are over 10 years old, technically outdated, and near the end of their serviceable life; Zeiss will cease to offer service contracts for them within 2 years. Second, the LSM 700 only has 2 channels, utilizes outmoded detection technology, and is mechanically very slow. Third, the LSM 710 has become unreliable and nonfunctional time has increased considerably. After a series of total break downs of the LSM 710, which threatened ongoing research projects, we were able to garner institutional support to acquire a Leica STELLARIS 5 confocal; installed in December 2020. The new instrument ushered in a next generation of technology to the Cellular Imaging Core, resulting in high demand and high satisfaction across our diverse user base. On its own, the single STELLARIS is not capable of supporting the 3000-plus annual hours of confocal imaging required by our users to advance their NIH-funded projects, nor is it able to support additional investigators who are being recruited to CHLA and will require this technology to establish their independent research programs. Thus, the institution has provided the support for the initial STELLARIS, but is in significant need of support to purchase a second STELLARIS 5 confocal before the Zeiss units become unserviceable and obsolete. After detailed testing of 4 confocal models (Leica, Nikon, Olympus, and Zeiss), we determined that the STELLARIS 5 is optimal for CHLA investigators with fixed- specimen applications because of its 4 sensitive hybrid light detectors (HyD S) that are each fully tunable with 1-nm precision in the range of 400-850 nm. It is also the best fit because the consistency of two STELLARIS 5 units maximizes efficiency for the user group in training, operating, and scheduling time on the instruments. In the Cellular Imaging Core, the requested STELLARIS 5 will be fully supported financially by CHLA and managed by an experienced PhD-level microscopist. This instrument will greatly benefit the entire confocal user base at CHLA through the ability to generate more imaging data than either of the two old systems, allowing us to meet the long-term objective of illuminating how organs develop and how aberrant structures lead to pediatric disease.