Our first project aimed at the determination of the average values of Mg in normal human brain (20 individuals, mean age 70 years). Ten brain parts were selected from both hemispheres. Determinations were carried out by inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry and instrumental neutron activation analysis methods. In order to investigate the precision and the accuracy of the methods five biological standard reference materials were analyzed. The present results show a non-homogeneous distribution of Mg in normal human brain. Regions corresponding to each other in both hemispheres show almost identical concentration. The second goal was to study the possible Mg concentration changes in Alzheimer's disease (nine patients, ten brain parts). Mg values are found to be significantly decreased in brain regions of diseased patients compared to the controls.