Peripheral-type benzodiazepine binding of [3H]Ro5-4864 at one, non-saturating concentration and activities of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) were measured in 7 cortical areas from postmortem brains of 18 patients with Alzheimer disease (AD), 12 age-matched controls, and 15 miscellaneous neurological cases. None of the chemical measures showed significant correlation with age, sex, or postmortem delay. As expected, ChAT and AChE activities were closely correlated with one another overall and within the AD and control groups, and the mean values for the AD group were significantly less than those in the controls in each of the cortical regions examined. Specific binding site densities were very variable from brain to brain and did not correlate with ChAT in any group or overall. By analysis of variance, however, binding site densities in the AD group were significantly higher than those in the controls. This difference was statistically significant (p less than 0.05) in Broca's area and the precentral and postcentral gyri, but not in the temporal gyri which generally have greater neuronal loss in AD. Of the 15 miscellaneous neurological cases, the Parkinson patients (n = 3) showed significantly higher binding densities than the controls but the multiinfarct dementia group (n = 5) did not. Single cases of Shy-Drager syndrome and sleep apnea showed a majority of values more than 2 standard deviations above the control means.(ABSTRACT TRUNCATED AT 250 WORDS)