This research is a framework of a big project aimed to the knowledge of human metabolism in hemodialysis patients. For reaching high sensitivity and obtaining accurate values for elements at very low concentrations Instrumental neutron activation analysis (INAA) was used for its characteristics to be a primary analytical method and because it does not require any chemical-physical pretreatment. The samples analyzed (160) are representative of groups of homogeneous population and specific matrices (hemodialysis fluids and whole human blood). The irradiation was performed in the rotating rack (Lazy Susan) of the Triga Mark II reactor of the R.C. Casaccia-ENEA at a neutron flux of 2.6 x 10(12) n cm(-2) s(-1) with an irradiation time of 12 h. The results on the hemodialysis fluids report the values and the behavior of selected trace elements: the levels of Br and Na show a decrease between the pre- and post-dialysis whereas Fe, K and Zn an increase. The other elements such as Cs, Rb and Se seem to keep constant between the two phases. Similar data are found for the whole human blood for the same selected elements. Finally, exploiting the INAA peculiarity it has been investigated the levels of trace and ultra-trace elements interesting from a toxicological (Hg, Ni, Sb) and nutritional (Co, Cr) point of view and seldom determined due to their analytical implications. Finally, a chemiometric investigation performed through dendrogram trees, Canonical discriminant analysis and principal component analysis, has evidenced the similar effects of the HF, HDF and BIC-treatments on the investigated fluids respect to the CAPD dialysis.