Aim : The main aim of the present study is to study whether chronic hy-poxia would alter the noradrenaline (NA)-evoked vascular responses in carotid circulation in rats. A second aim was to test whether the carotid autoregulatory response to NA-evoked rise in arterial blood pressure (ABP) is compromised by chronic hy-poxia or not. Further, the role of toni-cally synthesised nitric oxide (NO) in these responses was investigated. Study Design : the study was done using 2 comparable age groups of adult Wistar rats; the first were breathing normal 21% O₂ (normoxic; N), whereas the second were made chronically hypoxic (CH) by breathing 12% C>2 for 3 weeks, while they were growing from 7 to 10 weeks. In an­aesthetised rats, the carotid blood flow (CBF) and carotid vascular con­ductance (CVC) were recorded dur­ing a 3 min infusion of NA at a dose 2.5 ng kg'¹ to induce an acute rise in ABP to 150 mm Hg, the upper limit of autoregulatory range, before and af­ter a bolus dose of the nitric oxide synthase inhibitor, L-NAME (10mg kg-¹). Results : the NA-evoked rise in ABP was comparable in N and CH rats, but the increase in heart rate was more significant in CH rats. In CH rats, the NA-evoked rise in ABP was associated with a significant re­duction Jn CVC but with no change in CBF, whereas in N rats