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[Reference values for xenobiotics in biological matrixes: the state of the art].

The basic concepts of reference values of xenobiotics in biological matrixes have been extensively discussed over the last 3-4 years by transferring the principles from clinical chemistry. In this paper three topics of current interest, i.e. the control of variability factors, metanalysis procedure for production of reference values, the reference values as a part of the system of guide values, are dealt with. The control of variability factors is identified as the most important procedure to guarantee the quality and consequently the usefulness of the reference values. Metanalysis is not considered as a correct method to produce reference values, but rather a method to compare the investigation published and to compel the investigators to standardize their working methods. Lastly reference values should be considered as the first step of an integrated system of values (action levels, limit values) which enable us to correctly interpret the significance of biological monitoring.