The mitotic inhibitor colchicine inhibits the axonal flow of proteins in various types of neurons. A differential effect of colchicine on vasopressin-containing neurons compared to oxytocin-containing ones has been suggested, and a decline in vasopressin immunoreactivity in the neurohypophysial system of aged monkeys has been reported. In the present work, we examined the action of colchicine in 3- and 15-month-old rats. Treatment with colchicine decreased the number of oxytocinergic neurons in 3-month-old and 15-month-old rats by 9.5% and 11.1%, respectively. There was also a 30.1% decrease in the number of vasopressinergic neurons in untreated rats after 15 months. These results show that oxytocinergic and vasopressinergic neurons of the supraoptic nuclei are differentially affected by colchicine and aging.