Alterations in neurochemical activity in the paraventricular nucleus (PVN) of the hypothalamus may account for decreased intake of zinc-deficient diets. Male Sprague-Dawley rats were fed zinc-deficient (ZD) or zinc-adequate (ZA) diet for 14 d before samples of extracellular fluid in the PVN were collected by microdialysis or push-pull perfusion. A third set of rats was pair-fed (PF) an amount of ZA diet equal to the intake of ZD rats. Samples were collected over a 2-h period spanning the transition from light to dark. All rats then consumed the zinc adequate diet ad libitum for 3 d before a second set of samples was collected. The increase in extracellular norepineprhrine (NE) during h 1 of the dark period to 147 +/- 13% of baseline (P < 0.05) was apparent only in ZA rats at d 14. After the 3-d repletion period, the increase in NE at dark onset occurred in all three groups. An increase in extracellular neuropeptide Y (NPY) at dark onset to 174 +/- 32% of baseline in rats fed ZA (P < 0.01) was measured in all three groups at both d 14 and 17. Basal NPY concentrations were significantly elevated in PF rats on d 14 (7.45 +/- 2.01 vs. 0.58 +/- 0.23 pmol/L, P = 0.01) and returned to ZA levels by d 17. The activities of the NE and NPY systems in the PVN were altered in rats fed a zinc-deficient diet; however, it is unclear whether the disruption in the NE and NPY neural systems in the PVN results in the altered feeding behavior accompanying zinc deficiency.