The nucleus tractus solitarius/dorsal motor nucleus of the vagus nerve (NTS/DMV) area was perfused by the push-pull perfusion technique in anesthetized rats, and perfusates were assayed for arginine vasopressin (AVP) and oxytocin (OXT) immunoreactivity. As compared with controls, electrical stimulation of the ipsilateral paraventricular nucleus (PVN) resulted in increased amounts of both AVP (approximately 5-fold) and OXT (approximately 10-fold, P less than 0.05 each) in the perfusates. During the poststimulation perfusion period, peptide concentrations were found to return to control levels. Elevation of circulating AVP and OXT by an osmotic stimulus did not result in increases of AVP and OXT in NTS/DMV perfusates. These data suggest that AVP and OXT are released from NTS/DMV area fiber terminals during electrical stimulation of descending PVN neurons. Furthermore, they are consistent with the view that both peptides are involved as neurotransmitters in autonomic regulation.