To evaluate lead exposure among children living in border communities, the states of Arizona and New Mexico in the United States (US), and the states of Sonora and Chihuahua in Mexico collaboratively requested that the Centers for Disease Control and Prevention (CDC) provide technical assistance to document pediatric blood lead levels (BLLs) in children living along this part of the US/Mexico border. Two studies were conducted to evaluate BLLs of children aged 1-6 years. In 1998, 1210 children were tested in the Arizona/Sonora study; in 1999, 874 children were tested in New Mexico/Chihuahua. Overall geometric mean BLL was 32.5 microg/l (95% Confidence Interval 31.5-33.5) with BLLs ranging from below limit of detection to 320.0 microg/l. Mean BLLs were higher among children living on the Mexican side of the border (43.2 microg/l) compared to those on the US side (22.3 microg/l). Mean BLLs ranged from 14.9 to 31.2 microg/l at the US sites and from 26.9 to 55.2 microg/l at the Mexican sites. This study used a convenience sample and cannot be considered representative of the general population. Nonetheless, the range of mean BLLs among the sites and especially the higher mean BLLs among children living in the border communities in Mexico suggests different exposures to lead and warrants further attention.