Andean high altitude natives show higher arterial oxygen saturation (Sao2) during exercise in hypoxia, compared to acclimatized sojourners. In order to evaluate the effects of life-long exposure to high altitude on Sao2, we studied two groups of well-matched, self-identified Peruvian Quechua natives who differed in their developmental exposure to hypoxia before and after a 2-month training period. Male and female volunteers (18-35 years) were recruited in Lima, Peru (150 m). The two groups were: a) Individuals who were born and raised at sea-level (BSL, n=34) and b) Individuals who were born and raised at high altitude (BHA, n=32), but who migrated to sea-level as adults (>16 years old). Exercise testing was conducted using a submaximal exercise protocol in normobaric hypoxia in Lima (BP=750 mmHg, Fio2=0.12), in order to measure Sao2 (%), ventilation (VE L/min) and oxygen consumption (Vo2, L/min). Repeated-measures ANOVA, controlling for VE/VO2 (L/min) and sex during the submaximal protocol showed that BHA maintained higher Sao2 (%) compared to BSL at all workloads before (p=0.005) and after training (p=0.017). As expected, both groups showed a decrease in Sao2 (%) (p<0.001), as workload increased. Resting Sao2 levels were not found to be different between groups. The results suggest that developmental exposure to altitude contributes to the maintenance of higher Sao2 levels during submaximal exercise at hypoxia.