Blood lead levels (BLLs) were determined by Total Reflection X-ray Fluorescence in a randomly sampled population living in the metropolitan zone of Mexico Valley (MZMV) at the beginning of 2001. Blood was digested and iron extracted by methyl-isobutyl-ketone, the latter in order to improve the detection limit. The geometric mean was 2.00 μg dl −1, 91% lower than the one obtained in 1980 of 22.2 μg dl −1. It is well correlated with the lead concentration decrease in environmental samples in the same period. All values were lower than indicative levels of WHO and Mexican Norm. A quality control program was improved that includes the analysis of IAEA-A13 standard of animal blood. The result was within the certified confidence limits and also in good agreement with the reported mean concentration value.