The paraventricular nucleus (PVN) is known to have an important function in mediating a variety of behavioral and endocrine responses. In the present study, the responsiveness of the PVN to the effects of the coexisting neurotransmitters, neuropeptide Y (NPY), epinephrine (EPI) and norepinephrine (NE), was examined. Albino rats were each chronically implanted with a swivel brain-cannula that permits chemicals to be infused without disturbing the animals' ongoing behavior. When infused into the PVN, each of these neurotransmitters elicited a reliable feeding response during the first hour after injection. The response to EPI was significantly stronger than that of NE and NPY, while the latency to eat after injection was considerably longer for NPY as compared to the catecholamines. In tests with food absent, each of these substances also increased blood levels of corticosterone (EPI greater than NE = NPY) and vasopressin (NPY greater than EPI greater than NE) and revealed a significant positive correlation between circulating levels of these two hormones. In addition, EPI and NE, in contrast to NPY, caused a simultaneous rise in blood glucose, producing levels that were positively correlated with the hormones. No relationship, however, was detected between these endocrine changes and the rats' feeding-stimulatory responses. Together with other evidence, these results suggest that adrenergic as well as noradrenergic innervation to the PVN has a key role in the behavioral and endocrine systems of this nucleus and, moreover, that NPY generally mimics the effects of these catecholamines in the PVN.