Neutron activation analysis-electrothermal atomic absorption spectroscopy (ETA-AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) have been used for the determination of 46 elements in urine, 35 in blood and 26 in serum of unexposed Italian subjects living in the same region (Lombardy). The results allowed the proposal of reference values for various elements determined in more than 350 healthy subjects, these being Ag, Al, As, Be, Bi, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Se, Tl, V, Zn, in urine; Ag, As, Bi, Cd, Cr, Co, Cu, Hg, Pb, Se, Tl, Zn in blood; and Ag, Al, Be, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Se, Tl, V, Zn in serum (or plasma). For all other elements indicative values are suggested. In addition to the mean value and the "reference range", a "range of uncertainty" and an upper limit above which metabolic abnormalities could be expected have also been defined on the basis of simple statistical considerations.