X-ray microanalysis was performed on ultrathin sections of tissues from six rats, four of which having been exposed to experimental metabolic disorder by overdoses of NaCl and Ca-Vit. D2, respectively. It was demonstrated that the elements Cl, Si, P, S, Ca and traces of Fe are identifiable quantitatively in arteriolar walls of colon, heart and kidney even after conventional electron microscopic preparation (fixation, dehydration and Epon embedding). Depending on the pretreatment considerable differences in elemental quantities between animal groups were observed. The reliability of these findings must be confirmed by further tests on a greater number of individuals.