The validation process is essential in accredited laboratory medicine, but is rarely regarded as an issue in the preanalytical management. The aim of this study was to validate five kinds of lithium heparin vacuum tubes for routine clinical chemistry laboratory testing. Blood speci-mens from 100 volunteers in five different plasma vacuum tubes (Tube I: VACUETTE Ò , Tube II: LABOR IMPORT Ò , Tube III: S-Monovette Ò , Tube IV: PST Ò and Tube V: PST II Ò) were collected by a single expert phle-botomist. The routine clinical chemistry tests were performed on a Cobas Ò 6000 ̧501[ module. The sig-nificance of the differences between samples was statistically assessed at p \ 0.005. The biases from the different tubes were compared with the current desirable quality specifications. Basically, significant differences could be confirmed by RM ANOVA for the results of the clinical chemistry tests on the following components: glucose, urea, creatinine, alkaline phosphatase, amylase, aspartate aminotransferase, alanine aminotransferase, lac-tate dehydrogenase, total bilirubin, phosphate, Ca, Mg, Fe and K. Clinically significant variations as compared with the current desirable quality specifications were found for glucose, creatinine, amylase, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, Ca, Mg and K. In conclusion, our results do not support arbitrary interchange among brands of plasma vacuum tubes. Future investigations are needed to understand the reasons of these observations; in the meantime, we suggest that laboratory managers standardize the procedures and frequently eval-uate the quality of in vitro diagnostic devices.