The large, hyperchromic, cholinergic neurons of the nucleus basalis of Meynert (nbM) and the presence of senile plaques were quantified in postmortem brain tissue from 10 intellectually impaired schizophrenic patients, seven intellectually intact schizophrenic patients, seven control subjects, and three patients with Alzheimer's disease. The two groups of schizophrenic patients did not show any significant differences when compared with the control group in nbM cell density or in plaque frequency. The Alzheimer's disease patients showed the expected decrease in nbM neuronal density and increase in plaques compared with the controls. The data suggest that compromised cognitive function in schizophrenia is not associated with diffuse neuropathology of the basal forebrain cholinergic system.