We thank Dr D’silva and colleagues for their interest in our recent article in CHEST.1 Most asthma exacerbations are considered to be associated with viruses,2 and current guidelines do not advocate the use of antibiotics for exacerbations of asthma.2 Interestingly, Dr D’silva and colleagues only identified viruses in 36% of cases and bacteria in 24%. In COPD, where bacterial infection is implicated as a major cause of exacerbations, current evidence does not support the use of antibiotics in the management of mild to moderate exacerbations.3 Whether patients with asthma and bacterial-associated exacerbations benefit from antibiotic therapy is uncertain; however, further detailed analysis of the microbiology of asthma exacerbations using both standard and molecular techniques is warranted. We and others have found that procalcitonin is not strongly associated with an exacerbation of COPD1 or asthma,1 but is elevated in patients with pneumonia. It is, therefore, a good biomarker of a systemic inflammatory response to pneumonia and may have potential clinical utility in directing antibiotic therapy.4 Importantly, the value of procalcitonin might not be greater than the more widely available C-reactive protein. Controlled trials of antibiotics directed by biomarkers such as C-reactive protein or sputum cell counts at exacerbations of asthma and COPD are required. Biomarker-guided therapy is commonplace in other medical specialties, such as cardiology. This approach needs urgent investigation and to be embraced by respiratory medicine if we are to make a change in the management of exacerbations of airways disease.