The feeding response induced by the paraventricular nucleus (PVN) injection of norepinephrine (NE) in rats has been shown to correlate positively in magnitude with the level of circulating corticosterone. The present study examined the feeding responses induced by NE and clonidine (CLON) injected into the PVN and CLON injected intraperitoneally, as a function of diurnal cycle and also in adrenalectomized animals with and without peripheral corticosterone replacement. A periodicity in the effectiveness of PVN-injected NE and CLON, as well as intraperitoneal CLON, was observed, with a significantly stronger eating response occurring near the onset of dark period compared with the response produced in the early light period. Adrenalectomy abolished the feeding induced by each of these alpha-noradrenergic agonists, and acute corticosterone replacement restored the response. The feeding induced by intraperitoneally injected 2-deoxy-D-glucose was unaffected. These findings indicate the importance of corticosterone to the action of peripherally and centrally administered alpha-noradrenergic agonists and also suggest that the diurnal rhythm of corticosterone plays an important role in determining the rhythm for the feeding response induced by PVN alpha 2-noradrenergic activation.