This research, that is a framework of a big project regarding the knowledge of human metabolism in patients affected by renal disease, is aimed to assess the levels of some selected essential (Co. Fe. K, Na, Rb, Se and Zn) and non-essential elements (Br Cr, Cs, Fig, Ni and Sb) in different biological matrices such as whole blood, serum and urine, of three Italian sub-populations. The analytical methodology involved is the Instrumental Neutron Activation Analysis (INAA), a primary analytical technique: the samples (totally 144) were irradiated in the Triga nuclear reactor at the R.C.-Casaccia ENEA for 12 h at a neutron flux of 2.6 x 10(12) n x cm(-2) x s(-1). The results show a similar distribution for essential elements whereas quite different for non-essential elements. The statistical treatment has evidenced no differences among the samples grouping the subpopulations into unique one. In this way, the levels found can be considered "reference values" in the investigated matrices. (C) 2011 Elsevier B.V. All rights reserved.