In the article entitled "Automated Assay for the Determinationof Methylmalonic Acid, Total Homocysteine, and Related AminoAcids in Human Serum or Plasma by Means of MethylchloroformateDerivatization and Gas ChromatographyMass Spectrometry"by A. Windelberg, O. Årseth, G. Kvalheim, and P.M. Ueland(Clin Chem 2005;51:21039), a sentence in the sample preparationsection is incorrect. In the sentence reading "Aliquots (380µL) of the supernatant obtained after centrifugation (3min at 5800g) were transferred into an empty microtiter plateand mixed with 300 mL/L of water and 50 µL of pyridine;250 µL of 200 mL/L in toluene was then added", 300 mL/Lof water should read "300 µL of water" and "200 mL/L intoluene" should read "200 mL/L MCF in toluene".