Tibetan highlanders develop at altitude peak aerobic power levels (VO2peak) close to those of Caucasians at sea level. In order to establish whether this feature is genetic and, as a consequence, retained by Tibetan lowlanders, altitude-induced changes of peak aerobic performance (VO2peak) were assessed in four groups of volunteers with different ethnic, altitude exposure and fitness characteristics, i.e.: 8 untrained second-generation Tibetans (Tib 2) born and living at 1,300 m; 7 altitude Sherpas living at ~2,800-3,500 m; 10 untrained and 5 trained Caucasians. Measurements were carried out at sea level or at Kathmandu (1,300 m, Nepal) (PRE), and after 2-4 (ALT1), 14-16 (ALT2), and 26-28 (ALT3) days at 5,050 m. At ALT3, VO2peak of untrained and trained Caucasians were -31% and -46%, respectively. By contrast, VO2peak of Tib 2 and Sherpas were -8% and -15%, respectively. At ALT3, peak heart rates (HRpeak) of untrained and trained Caucasians were 148±11 and 149±7 beats min-1, respectively, blood oxygen saturations at peak exercise (SaO2peak) were 76±6% and 73±6%, and haemoglobin concentrations ([Hb]) were 19.4±1.0 and 18.6±1.2 g dl-1, respectively. Compared to Caucasians, Tib 2 and Sherpas exhibited at ALT3 higher HRpeak (179±9 and 171±4 beats min-1, P<0.001), lower [Hb] (16.6±0.6 and 17.4±0.9 g dl-1, respectively, P<0.001), and slightly but non-significantly greater average SaO2peak values (82±6 and 80±7%). The above findings and the time course of adjustment of the investigated variables suggest that Tibetan lowlanders acclimatise to chronic hypoxia more quickly than Caucasians, independent of the degree of fitness of the latter.