Monitoring is, in itself, an intervention which alters behaviour. The theoretical model developed by Glasziou et al. describes the complementary and evolving roles of periodic professional reviews and on-going patient self-monitoring.19 The monitoring of asthma with lung function and/or symptoms is cited as a well-defined exemplar of this concept. Our recent qualitative study suggests that people with asthma perceive a role for mobile technology in aiding transition from clinician-supported phases while control is gained, to effective self-management during maintenance phases.20 This approach resonates with two key health service policies: the drive for technological solutions to healthcare problems;21 and the importance of expert patients and self-management of long-term conditions.22,23 Our proposed trial tests the hypothesis that through engaging the patient in self-monitoring with timely biofeedback, mobile phone technology can improve the asthma control achieved at six months compared to usual paper-based monitoring.