Golgi-impregnated neurons in biopsy samples of the cerebral cortex (area 8) of patients with Alzheimer's disease (AD), Pick's disease (PD) and Creutzfeldt-Jakob disease (CJD), but not in control samples, have swellings in the proximal and mid regions of dendrites of pyramidal and non-pyramidal cells that differ from normal dendritic varicosities. Dendritic outgrowths, isolated or in clusters, and covered with spines occur only in neurons with reduced dendritic arbors mainly located in the vicinity of senile plaques. Degenerating pyramidal and non-pyramidal neurons, although distributed throughout the cerebral cortex in CJD and PD, predominate in layers II, III and VIb in patients with AD.