To the Editor.
—We applaud Dr Needleman and colleagues1 in their effort to expand the use of bone lead measurement to younger, non—occupationally exposed subjects and to study delinquent behavior as a new aspect of lead exposure's potentially far-reaching consequences. However, we feel that there are aspects of this work that require more discussion.As pointed out in their article, the individual K x-ray fluorescence (KXRF) measurements have large uncertainties. Owing to these uncertainties, the authors elected to present their data only in categorical form. Descriptive statistics, including the mean, and population variance would allow comparisons with other XRF studies of children and young adults.The description of the KXRF technique itself raises some questions. No mention was made that calibration standards below 10 μg of lead per gram of bone mineral (expressed as μg/g) were used. In our experience, a standard of 5 μg/g is important since this