To examine the possibility that senile dementia may be associated with a loss of noradrenergic neurons that innervate the cerebral cortex, we used a Quantimet 720 image analyzer to estimate the number of neurons in the nucleus locus ceruleus in elderly patients with the clinical diagnosis of senile dementia. In all but one case, the diagnosis was established histopathologically as senile dementia of the Alzheimer type (SDAT). In a subgroup characterized by a high dementia score and relatively young age at death, there was a loss of about 80% of locus ceruleus neurons. This loss of neurons indicates a deficit of noradrenergic innervation to cerebral cortex in a group of patients which may represent a variant of SDAT.