In Andean natives (NAT), the ventilatory response to hypoxia is blunted at rest but potential interaction with exercise has been little studied. Therefore, during three levels of submaximal exercise, 13 NAT were compared with 6 sojourners (SOJ) acclimatized at 4,360 m for an average of 7 months. Exercise ventilation was measured first breathing oxygen (PI(O(2)) 410 Torr) and then ambient air (PI(O(2)) 86 Torr). In SOJ ventilation was increased by hypoxia at all three exercise levels including the mildest. In NAT, however, the threshold for hypoxic sensitivity was displaced, but during exercise above this threshold hypoxia increased ventilation at a rate similar to that seen in SOJ. At the heaviest workload, ventilation was increased by hypoxia 18% in NAT compared with 30% in SOJ. Thus, during exercise Andean NAT do exhibit a ventilatory sensitivity to hypoxia, the magnitude of which is dependent upon exercise intensity.