In the article by J.T. Hindmarsh, L.
Oliveras, and D.C. Greenway,entitled "Plasma Porphyrins in the
Porphyrias" (Clin Chem 1999;45:10706),the HCl concentrations given
on page 1071 under "Calibratorsand controls" and "Extraction
procedure" in Materials and Methodsshould be in mol/L,
not mmol/L. The authors regret any confusionthis may have caused.