1. The ventilatory response to carbon dioxide was measured in a group of patients with chronic obstructive airways disease using a rebreathing method.
2. The slope of the carbon dioxide response curve was obtained by plotting the ventilation at successive half minutes against the corresponding mean end tidal Pco2.
3. The slope of the carbon dioxide response curve was positively correlated with (a) the FEV1 and (b) the reciprocal of the resting arterial Pco2, both these correlations being statistically significant.
4. Reference to FEV1 alone could explain more than 80% of the variation in the slope of the CO2 response curve. This explained variation was not significantly improved by the additional consideration of the resting arterial Pco2.
5. It was suggested that whatever the underlying complex mechanisms that determine the response to CO2, the FEV1 can be used as an empirical factor for the prediction of this response in patients with chronic obstructive airways disease.