In female mammals including rodents and humans, feeding decreases during the periovulatory period of the ovarian cycle, which coincides with a surge in circulating estrogen levels. Ovariectomy increases food intake, which can be normalized by estrogen treatment at a dose and frequency mimicking those during the estrous cycle. Furthermore, administration of estrogen to rodents potently inhibits food intake. Despite these well-known effects of estrogen, neuronal subtypes that mediate estrogen's anorexigenic effects have not been identified. In this study, we show that changes in hypothalamic expression of agouti-related protein (Agrp) and neuropeptide Y (Npy) coincide with the cyclic changes in feeding across the estrous cycle. These cyclic changes in feeding are abolished in mice with degenerated AgRP neurons even though these mice cycle normally. Central administration of 17-estradiol (E2) decreases food intake in controls but not in mice lacking the AgRP neurons. Furthermore, E2 treatment suppresses fastinginduced c-Fos activation in AgRP and NPY neurons and blunts the refeeding response. Surprisingly, although estrogen receptor alpha (ER␣) is the key mediator of estrogen's anorexigenic effects, we find that expression of ER␣ is completely excluded from AgRP and NPY neurons in the mouse hypothalamus, suggesting that estrogen may regulate these neurons indirectly via presynaptic neurons that express ER␣. This study indicates that neurons coexpressing AgRP and NPY are functionally required for the cyclic changes in feeding across estrous cycle and that AgRP and NPY neurons are essential mediators of estrogen's anorexigenic function.estrogen ͉ feeding P roper regulation of energy homeostasis and reproduction is fundamental for fitness and survival. Reproduction is an energy intensive process, and precise interaction of regulators for energy balance and reproduction allows coordinated regulation of these two processes. Leptin, a hormone secreted from adipose tissue, plays a critical role in both energy balance and reproduction. Leptin is produced proportional to body fat mass and it conveys the abundance of the body's energy stores to the brain, where it acts to regulate feeding and energy expenditure (1). A decline in leptin level signals a state of negative energy balance, which triggers robust counterregulatory mechanisms to increase feeding. One consequence of negative energy balance is induction of hypogonadonism and inhibition of reproductive function (2). Consistent with this notion, leptin deficiency results in profound hyperphagia and infertility in rodents and humans (1,(3)(4)(5).Estrogen, a hormone essential for sexual reproduction, plays a role in feeding and energy balance regulation. Serum levels of estrogen decline during negative energy balance (6) and estrogen deficiency or loss of function of estrogen receptor (ER) results in increased feeding and adiposity in rodents and humans (7-10). Feeding and body weight increase in ovariectomized females and estrogen replacement reverses such effects (11,1...