1. Changes in blood flow of the skin of the rabbit's ear and hind limb have been studied during arterial hypoxia by a calibrated heat conductivity method, together with changes in arterial pressure and aortic blood temperature. 2. There is little change in the blood flow of the hind‐limb skin during the early phase of arterial hypoxia, reflecting a balance between the local dilator effects of hypoxia and the increased constrictor activity mediated through the sympathetic nerves as a result of arterial chemoreceptor excitation. During more prolonged arterial hypoxia there is a small gradual dilatation of the vessels of the hind‐limb skin as a result of some diminution in the initial intensity of vasoconstrictor activity. 3. There is much more extensive vasodilatation in the ear than in the hind‐limb skin during arterial hypoxia. Vasoconstrictor activity is slight in this region. Comparison of the ear responses to arterial and to primary tissue hypoxia suggests that in the former type of hypoxia stimulation of the arterial chemoreceptors inhibits thermoregulatory vasoconstriction to the ear, whilst in the latter type of hypoxia baroreceptor reflexes maintain or intensify it.