The hypothalamic supraoptic and paraventricular nuclei form the neurosecretory system and synthesize the neurohormones oxytocin and arginine-vasopressin. The senescence-accelerated mouse is a model of rapid aging that displays senile amyloidosis and memory problems. This paper presents the characterization of the neurosecretory system and describes the presence of a bilateral constant cluster of neurosecretory neurons in these mice. The stereologic analysis revealed that these groups contain 197 +/- 18 cells (87% synthesize arginine-vasopressin and 13% oxytocin). The presence of these clusters of neurosecretory neurons suggests that these mice could present greater neurohormone synthesis, increasing the deleterious effects of accelerated aging in this strain.