['The purpose of this trial was to establish whether changes in resting oxygen saturation (Spo(2)) during ascent of Jade Mountain is useful in predicting acute mountain sickness (AMS). AMS-risk factors were also assessed.', 'A prospective trial was conducted on Jade Mountain, Taiwan from October 18 to October 27, 2008. Resting oxygen saturation (Spo(2)) and heart rate (HR) were measured in subjects at the trail entrance (2610 m), on arrival at Paiyun Lodge (3402 m) on day 1, and at Paiyun Lodge after reaching the summit (3952 m) the next day (day 2). AMS was diagnosed with Lake Louise criteria (AMS score ≥4). A total of 787 subjects were eligible for analysis; 286 (32.2%) met the criteria for AMS.', 'Subjects who developed AMS had significantly lower Spo(2) than those who did not at the trail entrance (93.1% ± 2.1% vs 93.5% ± 2.3%; P = .023), on arrival at Paiyun Lodge on day 1 (86.2% ± 4.7% vs 87.6% ± 4.3%; P < .001), and on the return back to the Paiyun Lodge after a summit attempt on day 2 (85.5% ± 3.5% vs 89.6% ± 3.2%; P < .001), respectively. Trekkers with AMS were significantly younger (40.0 vs 43.2 years; P < .001), and had less high altitude (>3000 m) travel in the previous 3 months (29.9% vs 37.1%; P = .004).'] Does change in oxygen saturation predict acute mountain sickness on Jade Mountain?