This proposal concerns the application of new technologies and design strategies for the purpose of improving the precision of K x-ray fluorescence (KXRF) bone lead measurement. This non-invasive technique has been used to assess long-term lead exposure in some adult populations. Applications to children have been limited. Of particular concern for KXRF studies of children, and to a lesser extent for studies of adults, has been the precision of the bone lead measurement. The current proposal seeks to address these concerns by improving the precision of the KXRF technique. This will be accomplished through the following experimental aims: (1) Apply two recently introduced digital signal processing units within a KXRF bone lead system and compare their performance with conventional components. (2) Use the MCNP4B Monte Carlo computer code to simulate a variety of KXRF system changes;. perform experimental testing on those changes identified as most promising. (3) Develop an improved KXRF bone lead measurement system with a digital signal processor and new system set-up; characterize the improved system parameters. Long-term goals of the proposal are to enhance the utility of the technique as an indicator of lifetime lead absorption, for applications such as epidemiological studies of chronic lead exposure in adults and children, lead kinetic computer modeling, and exposure assessment of children.