The central cardiovascular effects of neuropeptide Y (NPY) have been investigated by microinjection of the peptide into the hypothalamic paraventricular nucleus (PVN) of conscious rats. NPY (100 ng) elicited a significant bradycardia in both Long Evans (control) rats (-27 +/- beats/min) and vasopressin-deficient Brattleboro rats (-19 +/- 6 beats/min). There was a slight fall in systolic blood pressure in both strains which was significant only in Long Evans rats. A higher dose of NPY (1000 ng) had no significant effect on blood pressure or heart rate, but produced a marked behavioural response characterized by initiation of foraging behaviour. These results provide further support for a role for NPY in central cardiovascular regulation, but provide no evidence of an indispensable involvement of vasopressin-containing pathways in the observed responses.