Criteria for reference value assessment of elements in human tissues. 
The availability of updated and reliable reference values for elements in biological tissues and fluids plays a key role in the correct planning and performance of clinical, toxicological and environmental studies.  The basic principles for a proper analytical approach in order to obtain such data are outlined.  This in turn should significantly reduce the wide range of figures reported for most elements as "normal" intervals in the scientific literature.  Some applications of these guidelines are illustrated in detail in the case of human lungs, liver and kidneys for which tentative reference values are assessed for a number of minor and trace elements, namely, Al, Ba, Cd, Cr, Cu, Li, Mg, Mn, Pb, Sr, V and Zn.