Lead is a central nervous system poison. Healthy People 2010 established a target blood lead level (BLL) for children of 0 μg/dL by 2010, but is silent with regard to any changes in BLLs standards for working age adults. In this paper, the relation of BLL to performance on two neurobehavioral tests was assessed in working age adults (N = 4909; Age 20 to 59 years; 51.4% Female) employing data from the Third National Health and Nutrition Survey (NHANES 111). Multiple linear regression analyses indicated a significant effect of BLL on time taken to complete an attention demanding cognitive task (Symbol Digit Substitution Task, SDST) but not accuracy of performance of the SDST or simple reaction time, after controlling for confounding variables of age, sex, race-ethnicity, and education. Persons with BLL ≥5 μg /dL took longer (multivariate adjusted mean = 23.6 Sec, SE = 0.30) compared to individuals with BLLs <5 μg /dL (mean = 22.5 Sec, SE = 0.14). The results suggest that lead burden in working age persons impairs central nervous processes involving executive mental functions (decision speed and attention). The findings, if confirmed by case control and or cohort studies would indicate a need to reconsider currently accepted lead levels in working age adults.