The Clinical Trial Readiness for Rare Diseases, Disorders, and Syndromes (R21 Clinical Trial Not Allowed) research funding program from the National Institutes of Health supports clinical projects that address critical needs for clinical trial readiness in rare diseases. The initiative seeks applications that are intended to facilitate rare diseases research by enabling efficient and effective movement of candidate therapeutics or diagnostics towards clinical trials, and to increase their likelihood of success through development and testing of rigorous biomarkers and clinical outcome assessment measures, or by defining the presentation and course of a rare disease to enable the design of upcoming clinical trials. The R21 exploratory/developmental grant supports investigation of novel scientific ideas or new model systems, tools, or technologies that have the potential for significant impact on biomedical or biobehavioral research. Applications are open to researchers at US-based research institutions. The award provides up to 275,000 USD for up to 2 years. Opportunity ID: PAR-23-159. The next letters of intent are due on September 17, 2023 and full applications are due on October 17, 2023.