SUMMARY1. The effects of neuropeptide Y (NPY) and related peptide fragments on blood pressure and vagal action at the heart were compared in the anaesthetized rat.2. A change in vagal action was taken as a measure of presynaptic activity and a change in blood pressure was taken as a measure of postsynaptic activity.3. NPY, NPY‐(13‐36) and a stabilized 13‐36 analogue of NPY (ANA NPY) all exerted pressor actions and attenuated vagal action at the heart.4. On the basis of different potencies demonstrated for the pressor and vagal inhibitory actions of these peptides, the results are consistent with the proposal that there are two populations of NPY rece