Clinical asthma management is limited by the lack of straightforward and clinically applicable techniques to assess control and appropriately adjust therapy. The availability of biomarkers associated with airway caliber, responsiveness, or inflammation has prompted interest in the application of these measures as surrogate asthma end points in clinical trials. Use of a biomarker as a surrogate outcome in practice is most appropriate in settings in which the effects of therapy on clinical disease, as experienced by patients, are fully captured by that biomarker. Recent studies suggest that although asthma therapies can alter various biomarkers, the relationship between these biomarker changes and important clinical outcomes is inconsistent. Because symptom-driven titration of therapy is feasible and effective, additional data demonstrating clinically important benefits of biomarker-driven care in asthma are needed to justify the logistic and economic burdens associated with clinical dissemination of these techniques.