Various observations reported in the literature suggest that the so-called Alzheimer changes of the intracellular neurofibrils in senile and presenile conditions are associated with dehydration.In the present experiments rabbits' brains were dehydrated in vivo by intravenous administration of 25% glucose solution. Microscopic examination showed that in some nerve cells, irregularly scattered in the brain, the intracellular argentophile fibres become coarse, and have a tendency to become matted strands. The nucleus remains intact. These changes correspond to the initial stages of Alzheimer's cell change in man as encountered in senile and presenile conditions. These findings are discussed in the light of the literature on this subject.The histological findings in experimental hydration are also reported.