Severe analytical problems are associated with the analysis of heavy metals at very low levels in biological samples. This
impose a high degree of sophistication of the NAA involving treatment of the sample before irradiation such as chemical separations,
physical treatments and biochemical fractionation, the experimental evaluation of interfering nuclear reaction as well as
the development of post-irradiation radiochemical separation. This paper treats of the problem related to the NAA of trace
elements in environmental biochemical toxicology focussing attention of the sources of the elements during the analysis. Typical
results and short discussion for every step of the analysis are reported.