At present, search for the causes of neurodegenerative diseases represents a major topic in brain research. Acquired disturbances of cell metabolism are supposed to be a cause of the two most important neurodegenerative disorders in ageing, like senile dementia of the Alzheimer type and Parkinson's disease, resulting in measurable decreases of in vivo and post mortem cerebral glucose metabolism. Accumulating evidence indicates that insulin plays an important role in the regulation of brain glucose homeostasis in the central nervous system and has trophic effects on neurons. It has been suggested that the reduction of brain glucose metabolism in neuro-degenerative disorders may be related to a defect of the neuronal insulin-insulin receptor-interaction. It will be the aim of our study to demonstrate whether there exist any changes in the content of insulin, its receptor and/or in the functionality of the insulin receptor and its signal transduction in neurodegenerative disorders as Alzheimer's and Parkinson's disease.