Our primary aim is to provide a descriptive approach to the analysis of counts of plaques and tangles by different readers. We wanted to find out whether subjects with minimal training can count plaques and tangles in histological specimens of patients with Alzheimer's disease and controls. Two experienced neuropathologists trained three student helpers to recognize plaques and tangles in slides obtained from autopsy material. After training, the students and pathologists examined coded slides from patients with Alzheimer's disease and controls. Some of the slides were repeated to provide an estimate of reliability. Each reader read four fields which were averaged to obtain estimates of plaque and tangle counts. Raters are compared on four aspects of concordance: location, scale, precision and accuracy. Precision and accuracy are combined to provide an estimate of concordance. We conclude that subjects with minimal training can be taught to count plaques and tangles. Concordance with the neuropathologists was somewhat greater for tangles. This paper also provides a methodology for comparing raters.