To elucidate the pathogenetic significance of neurofibrillary tangles in Alzheimer's disease, the dendritic tree of tangle-bearing and unaffected pyramidal cells of area CA1 of the hippocampus was morphometrically examined. Golgi-stained neurons were assessed which were deimpregnated and counterstained with Congo red to visualize neurofibrillary tangles. The study revealed that tangle-bearing neurons have more extensive apical dendritic trees than tangle-free neurons. It is concluded that metabolic processes associated with the formation of neurofibrillary tangles may increase neurotrophic activity on a single cell level and counteract the cellular degeneration process.