The prenatal environment has been shown to cause a variety of effects in the offspring that persist into adulthood1. This phenomenon of developmental programming often results in altered vascular function leading to hypertension. We have previously demonstrated that chronic hypoxia in utero (CHU) induces changes in vascular regulation in male offspring (CHUM) by altering the functional role of NO2, however, there is no information on how female offspring (CHUF) are affected. It is also generally accepted that females have a lower risk of developing cardiovascular disease than males3 but it is not known how this is affected by developmental programming. Pregnant female Wistar rats were housed in a hypoxic chamber (maintained at 12% O2) during days 10-20 of pregnancy. Dams were then moved into air for the remainder of pregnancy and the offspring were reared in air. Acute experiments were performed, under anaesthesia (Alfaxan 12mg.kg-1.hr-1), on normal (N) and CHUF rats (9-10 weeks old) to assess the cardiovascular responses to acute hypoxia (breathing 8% O2) under 3 conditions: Control, after blocking NO synthase (L-NAME) and after restoring baseline vascular tone with NO donor (SNP). Vasodilator responses were assessed in the hindlimb by changes in integrated femoral vascular conductance (IntFVC). Samples of Tibialis Anterior (TA) were taken for eNOS expression by Western blotting. Arterial blood pressure (ABP) in normoxia was higher in CHUF than N rats (127±3 vs 112±3 mmHg; mean±SEM; P<0.01). Breathing 8% O2 induced a fall in ABP and skeletal muscle dilatation in both groups, but the increase in IntFVC was significantly smaller in CHUF (0.8±0.2 vs 2.2±0.6 CU in N rats; P<0.05). L-NAME induced a significant increase in ABP only in N rats, and attenuated the hypoxia-induced increase in IntFVC in N (0.7±0.1 CU; P<0.05) but not CHUF rats (0.6±0.1 CU). Infusion of SNP restored baseline IntFVC in both groups. Moreover, the hypoxia-induced increase in IntFVC was restored in N (2.2±0.3 CU). but augmented in CHUF (2.7±0.6 CU; P<0.001). No differences were found between N and CHUF in eNOS expression in TA muscle. The higher baseline ABP and lack of effect of L-NAME in CHUF suggests they exhibit endothelial dysfunction resulting from decreased NO bioavailability; our data suggest this does not result from reduced eNOS protein expression. Importantly, L-NAME did affect baseline ABP in CHUM2. That exogenous NO during NOS inhibition augmented the hypoxic dilatation in CHUF raises the possibility that their decreased NO availability results from O2- generated by eNOS which attenuates the role of NO in hypoxia-induced muscle vasodilatation. In conclusion, developmental hypoxia provides a programming stimulus that affects endothelial regulation of vascular tone in ways that are gender specific.