The commissioning of healthcare services is increasingly linked to the availability of rigorous evidence of clinical and cost effectiveness. In the current climate, ‘rigorous evidence’ is synonymous with the randomised controlled trial (RCT). Consequently, health technologies are often funded in preference to service developments due to an imbalance in the availability of strong evidence to support service developments. Simultaneously, there is an increasing policy emphasis on patient choice and individualised care in the NHS. In this paper Bill Watson, Susan Procter and Wendy Cochrane discuss the implications of using experimental methods in service development research, with reference to an ongoing RCT evaluating the component parts of pulmonary rehabilitation in people with chronic obstructive pulmonary disease (COPD)