In hyperventilation syndrome (HVS), hyperventilation is often provoked by exercise. This study was undertaken to investigate gas exchange parameters and their correlation to arterial blood gas values in HVS patients during exercise. Ventilatory equivalents for oxygen (VE/VO2) and carbon dioxide (VE/VCO2) were significantly higher in HVS patients than in the controls. (VE/VO2) during light exercise (40-50 W) was 23.1 +/- 2.7 (n = 10) in the controls and 35.2 +/- 8.2 (n = 10) in the HVS group (p < 0.01). VE/VCO2 during light exercise was 30.0 +/- 3.3 in the controls and 41.8 +/- 6.0 in the HVS group (p < 0.01). In HVS, significantly correlations were observed between VE/VCO2 and PaCO2, and between VE/VO2 and PaCO2 during both light and maximal exercise (p < 0.02). The findings suggest that exercise testing can be used to aid HVS diagnosis without invasive arterial cannulation.