The postmortem stability of alpha-bungarotoxin binding sites was examined in the brains of mice handled under conditions designed to simulate the handling of human autopsy material. No significant changes in the concentration of binding sites were evident up to 24 h after death. No correlation between the number of binding sites and the delay period between death and autopsy was found in studies of frontal cortex or mid-temporal gyrus from normal humans or cases of dementia of the Alzheimer type. Samples of mid-temporal gyrus from demented patients show a significant reduction in the number of binding sites.