Five male alpacas native to high altitude, of approximately 40 kg, were studied first at 3,300 m and again after a 3-month sojourn at sea level. Measurements were made with the animals standing, unsedated and breathing air. Cardiac output was measured by the dye dilution technique. Blood gas tensions and contents were measured in arterial and mixed venous blood. Blood samples were also equilibrated with different oxygen tensions to construct O2-Hb dissociation curves. The P50 was 17.8 and 19.7 torr at 3,300 m and at sea level, respectively. The higher P50 values at sea level were associated with higher values of base excess. PaO2 was lower at 3,300 m but Sa02, was always above 90%. No significant changes in [Hb], Hct, Q̇, CaO2 and CvO2, with changes in elevation were observed. PaCO2 tended to be lower at altitude indicating a mild hyperventilation. The values of PvO2 were lower than those reported for other mammals but similar to those of the llama. A higher PvO2 was measured in the alpacas at sea level. The alpaca under conditions of chronic hypoxia presents only minor cardiorespiratory adjustments suggesting the possibility of tissue characteristics well suited for life at high altidude. © 1976.