Accelerator mass spectrometry (AMS) is a sensitive mass spectrometric method for detecting and quantifying rare long-lived isotopes with high precision. This technique is widely employed in the earth and environmental sciences and is now being applied in the biomedical fields. AMS is primarily used to in the areas of pharmacology and toxicology to investigate the absorption, distribution, metabolism, and excretion of radiolabeled drugs, chemicals, and nutrients, as well as in the detection of chemically modified DNA and proteins in animal models and humans. The exquisite sensitivity (10-18 mol) of AMS allows for the use of low chemical and radioisotope doses and relatively small sample sizes, which enables studies to be performed safely in humans, using exposures that are environmentally or therapeutically relevant. Series: "Lawrence Livermore National Lab Science on Saturday" [Science] [Show ID: 33431]