Toxic trace elements such as lead (Pb) and Cadmium (Cd) can be measured non‐invasively in humans by radiation physics techniques, particularly x‐ray fluorescence and neutron activation. An analysis is usually made of the content of a particular organ, representing the principal storage site of the element in question. For example, Pb is measured in bone, whereas Cd is measured in liver and kidney. Measuring stored quantities of these elements has contributed to assessment of health effects of chronic occupational and environmental exposure. In addition knowledge of the elemental metabolism has been significantly extended. Results ofinvivostudies have also contributed to assessment and regulation of workplace exposure. Analogous methods are in use or under development forinvivoassay of mercury, aluminum, gold, platinum, and manganese. The principles of these measurements will be outlined and illustrative applications for Pb and Cd will be discussed.