The National User Resource for Biological Accelerator Mass Spectrometry (AMS) is the only User Resource of its type in the United States. It provides ultra-high sensitivity, quantitative isotopic analysis for biomedical researchers measuring very low-level radioisotopes (primarily 14C). With over 30 years of expertise in the development and application of AMS for biomedical sciences, the User Resource continues to enhance AMS analysis through utilization of new methods, instrumentation, and training for researchers.