We are grateful to Drs Ju-Shao Yen and Tzung-Hai Yen for their appraisal1 of our article.2 The authors suggest that plasma samples are suboptimal for body exposure evaluation compared to whole-blood samples, based on a study in which within- and between-variation of various lead biomarkers were compared using inductively coupled plasma mass spectrometry equipment introduced in 2001.3 Given the tremendous and still ongoing improvements in this field, the only valid conclusion of the study from Sommar et al3 is that total variance in whole-blood lead concentrations is largely attributable to inter-individual differences; in terms of plasma concentrations, the equipment that was used does not allow for valid conclusions that can be extended to more recent equipment.