Blood lead measurements were obtained on 13,642 persons aged 1 year and older who participated in Phase 2 of the Third National Health and Nutrition Examination Survey (NHANES III) from 1991 through 1994. NHANES III is a national representative survey of the civilian, noninstitutionalized U.S. population. The overall mean blood lead level for the U.S. population aged 1 year and older was 2.3 microgram/dl, with 2.2% of the population having levels >=10 microgram/dl, the level of health concern for children. Among U.S. children aged 1-5 years, the mean blood lead level was 2.7 microgram/dl, and 890,000 of these children (4.4%) had elevated blood lead levels. Sociodemographic factors associated with higher blood lead levels in children were non-Hispanic black race/ethnicity, low income, and residence in older housing. The prevalence of elevated blood lead levels was 21.9% among non-Hispanic black children living in homes built before 1946 and 16.4% among children in low-income families who lived in homes built before 1946. Blood lead levels continue to decline in the U.S. population, but 890,000 children still have elevated levels. Public health efforts have been successful in removing lead from population-wide sources such as gasoline and lead-soldered food and drink cans, but new efforts must address the difficult problem of leaded paint, especially in older houses, as well as lead in dust and soil. Lead poisoning prevention programs should target high-risk persons, such as children who live in old homes, children of minority groups, and children living in families with low income.