Since the turn of the century studies have suggested that clinical deterioration in Alzheimer's disease (AD) is accompanied by a gradual increase in both the size and numbers of senile plaques (SP's). Our study investigated the 'mass effect' of SP's on the morphometry of adjacent neurons. For this purpose, we used a computerized image analysis system to study pyramidal cells from the hippocampus of ten AD patients, ten demented schizophrenic (SC) patients and ten cognitively impaired non-AD/non-SC control patients with. We examined cell shape, area and disarray and quantitated the number of SP's and neurofibrillary tangles (NFT's) in the CA1 subfield of the hippocampus. Our results indicated no significant differences between groups for measurements of neuronal shape, size, or disarray. Contrary to earlier reports, our results noted no evidence of pyramidal cell disarray in schizophrenic patients. Our results suggest that SP's incorporate, rather than displace, their surrounding neuropil.