The Texas-Mexico border population has a high prevalence of neural tube defects (NTDs). In 1998, in an effort to reduce the risk of NTD-affected pregnancies, the US Food and Drug Administration mandated folic acid fortification of enriched grain products. Since then, the median serum folate and red blood cell (RBC) folate levels of US women aged 15 through 44 years has risen. During 1995 through 2000, serum and RBC folate levels of 170 Mexican American women residing on the Texas-Mexico border who had delivered live, normal infants within the previous 3 months were tested. The median serum folate levels rose 46%, and RBC folate levels rose 44%. The increase suggests that food fortification may be affecting folate levels among populations with economic and cultural barriers to consuming fortified foods. However, more data are needed before we can assess the impact of food fortification on NTD rates on the border.