Air travel has increased steadily over the last decade, and its effect on the health of passengers has been the subject of much debate. There is a paucity of evidence on the effects of air travel on oxygen saturation in general populations. The peripheral oxygen saturation and pulse rate of 84 passengers, aged 1-78 years, were measured by pulse oximetry at round level and altitude during air travel. There was a statistically significant reduction in oxygen saturation in all passengers travelling long haul and short haul flights (p < 0.05). The mean [range] (SD) SpO(2) for all flights at ground level was 97% [93-100] (1.33) and at cruising altitude 93% [85-98] (2.33). Fifty-four per cent of passengers had SpO(2) values of 94% or less at cruising altitude. This is a value which may prompt physicians to administer supplemental oxygen in hospital patients.