A Working Group of the European Group for the Evaluation of Reagents and Analytical Systems in Laboratory Medicine proposes, after detailed study of the advantages and disadvantages of available strategies, the following quality specifications for analytical systems for clinical chemistry. Total imprecision should be: (a) less than one-half of the average within-subject biological variation, or (b) less than the state of the art achieved by the best 0.20 fractile of laboratories, whichever is the less stringent. The second approach may be used when data on biological variation do not exist. Inaccuracy should be: (a) less than one-quarter of the group (within- plus between-subject) biological variation, or (b) less than one-sixteenth of the reference interval, when data on group biological variation do not exist, or (c) less than twice the ideal imprecision, if the above specifications are too demanding.