Measurement of inspiratory capacity (IC) as a marker of dynamic lung hyperinflation has been shown to correlate with dyspnea and exercise performance in stable COPD, and is therefore of potential utility in the management of this condition. We have examined whether similar relationships exist during acute exacerbations of COPD and asthma in order to determine whether there is a role for IC monitoring in acute management of these conditions. Eight patients with COPD and ten with asthma requiring hospital admission for acute exacerbations were studied with spirometry (including IC) at admission and at discharge and had concurrent self-perceived resting dyspnea ratings recorded. Over the admission there were significant improvements in resting dyspnea for the COPD group only, and improvements in spirometric indices in the asthma group only. No significant correlations were found between changes in dyspnea and changes in IC, in terms of acute responses to bronchodilator and in response to treatment over the hospital admission. These data suggest that dynamic hyperinflation during acute exacerbations of COPD and asthma is not as sensitive an indicator of resting dyspnea as in stable disease. A role for IC monitoring in the management of acute exacerbations of these diseases has not been identified.