In a sample of consecutively received, 4 demented and 4 age-matched nondemented brains, the total cortical area covered by plaque-like A beta amyloid and butyrylcholinesterase deposits was measured at two regions of the temporal cortex with the help of computed densitometry. Demented as well as age-matched nondemented brains contained A beta and butyrylcholinesterase-positive plaques. The total cortical area covered by the A beta precipitates was higher in demented individuals but there was overlap with the values seen in the specimens from nondemented individuals. The proportional plaque area displaying butyrylcholinesterase reactivity was very significantly and five fold to sixfold higher in the demented than in the nondemented group and there was no overlap between the two populations. Diffuse A beta deposits in nondemented elderly brains may represent a benign or preclinical stage of plaque deposition with relatively little pathological effect on brain tissue and mental function. Our results suggest that the progressively more extensive butyrylcholinesterase reactivity of plaques may participate in their transformation from a relatively benign form to pathogenic structures associated with neuritic degeneration and dementia.