Adverse health effects from exposure to lead are now recognized to be among industrialized society's most important health problems. This report, prepared by the National Research Council's Committee on Measuring Lead Exposure in Critical Populations, concurs with new findings issued by the Centers for Disease Control which state that lead concentrations above 10 micrograms per deciliter of whole blood in pregnant women, fetuses, and young children may be associated with toxic effects. Chapter 1 serves as an introduction and provides historical background on lead exposure concerns. Chapters 2 and 3 summarize the toxicity of lead and sources of exposure to lead for sensitive populations. Chapter 4 deals with lead in blood and other physiological media and describes the monitoring of biological markers that indicate exposure, markers of early toxic effects, and markers of susceptibility. Chapter 5 assesses techniques for quantitative measurement of the biological markers of exposure and effect, while chapter 6 presents the committee's conclusions and recommendations to improve the monitoring of lead in sensitive populations. Contains 74 pages of references. (MDM)