At two altitudes (3,600 and 5,200 m), resident native women (A) showed higher PAco₂ and Paco₂, lower PAO₂ and PaO₂, as well as lower arterial pH, than native males (C) of similar age. Resting minute ventilation (VE/m²), tidal volume (VT) and respiratory frequency (f) were similar. The differences in the alveolar-arterial gas tensions in A stem from larger dead space (VDS), VDS/VT and reduced alveolar ventilation (VA). Newcomer females (B) at both altitudes differed from new- comer males (D) in regard to larger resting VA, f and smaller VT. No differences were demonstrated in size of VDS, VDS/VT or VO₂/BSA; but PAco₂ and PacO₂ were lower, PAO₂ and Pa higher and VE/VO2 and VA/VO₂ (ventilatory equivalents) above those for resting newcomer males. A contrasted with resting B at 3,600 m (12,200 ft), showing higher PAco₂ and Paco₂, lower Pao₂ and arterial pH, reduction in VA and larger VDS/VT. Both C and D at 3,600 and 5,200 m during steady-state 60-W (367 kg/m/min) exercise showed lower PAco₂ and Paco₂, higher arterial pH, smaller VDS and higher VE/VO₂ than exercising A. The latter differed from C exercising at the same work load in that VE/m² and VA were reduced, PAco₂ and Paco₂ were higher, Pa-ao₂ gradients were wider, pH was lower and VDS as well as VDS/VT were larger. Contrasted with B during steady-state 60-W exercise at both altitudes, D showed consistently smaller VDS and larger VA. While both C and A had higher resting f than D, f of newcomer females at La Paz was higher than that of A. Control of ventilation by relating VE to Pao₂ and Paco₂ at rest and exercise at both altitudes showed marked attenuation of hypoxic and hypercapnic drives, particularly in the native resident female, suggesting diminished peripheral chemoreceptor function.

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