Peptide YY (PYY) is produced in L cells of the intestine and is released after eating. PYY circulates in a truncated form designated PYY(3-36). PYY(3-36) is thought to be a physiologic anorexigenic peptide. The objective of the current study was to test the effect of exogenous PYY(3-36) on food intake in non-human primates exposed to different ovarian steroid milieus. The study was conducted in four ovariectomized cynomolgus monkeys replaced with estrogen alone for 2 weeks followed by estrogen in combination with progesterone for 2 weeks to mimic the menstrual cycle. The effect of PYY(3-36) on food intake was tested during each week of the simulated menstrual cycle by comparing the 2 h food intake following intracerebroventricular (icv) injection of artificial cerebrospinal fluid (aCSF) or PYY(3-36). Despite considerable variation in food intake following aCSF, PYY(3-36) consistently inhibited food consumption, except during week 2 of estrogen plus progesterone replacement. PYY(3-36) reduced food consumption by 16.2 g (95% confidence interval (CI)=4.5-27.9 g) and 26.6 g (95% CI=7.3-45.9 g) in weeks 1 and 2 respectively of estrogen only treatment and by 38.2 g (95% CI=26.1-50.2 g) in week 1 of estrogen plus progesterone treatment. In contrast, PYY(3-36) injected in week 2 of estrogen plus progesterone did not consistently inhibit food intake (13.1 g; CI=-49.5-75.7). This is the first study to report the effect of PYY(3-36) on food consumption in female monkeys. We conclude that icv administration of PYY(3-36) has a strong anorexic effect in female cynomolgus monkeys and that sensitivity to PYY(3-36) may be influenced by the ovarian steroid milieu.