Arterial haemoglobin saturation during exercise in healthy young women [eight subjects mean (SEM) age 20.8 (1.8) years] was measured to confirm the theory that young women experience exercise-induced arterial hypoxaemia (EIAH) at a lower relative percentage of maximal oxygen uptake (VO2max) than has been documented in their male counterparts. To determine if flow limitation [the percentage of the tidal volume (VT) that met or exceeded the boundary established by multiple maximal expiratory manoeuvres] and/or post-exercise lung diffusing capacity are linked to EIAH in women, and to investigate the influence of exercise intensity and duration on post-exercise carbon monoxide lung diffusing capacity (DL, CO), these parameters were measured during and after three exercise tests (incremental test until exhaustion, 5 km run and 5 km run with sprint). All subjects experienced physiologically significant EIAH (a fall of more than 3% in oxygen saturation of arterial blood from levels at rest) and seven subjects experienced flow limitation during the VO2max protocol [mean (SD) 12.2 (8.8)% of VT]. Even though there was no significant relationship between aerobic capacity and the degree of flow limitation (r=0.33, P>0.05), the flow limitation was related to absolute ventilation in the subjects studied (r=0.82, P0.05), however there was a strong correlation between the extent of flow limitation (% of VT) and EIAH (r=0.71). Significant decreases in DL, CO lasted for up to 16 h after each of the exercise tests (PPD L, CO with the percentage of VO2max attained during the various tests being significantly related to the fall in DL, CO for 1, 2, 3, 16 and 24 h after exercise (P<0.05). As the appearance of flow limitation closely coincided with the appearance of EIAH, the results from the present study suggest that flow limitation is a contributing factor to EIAH in women although the exact mechanism remains unclear.