Pragmatic clinical trials (PCTs) are today an increasingly prominent means of measuring the ‘effectiveness’ of healthcare interventions in ‘real world’ clinical settings, in order to produce evidence on which to base regulatory and clinical decision‐making. Although several sociological studies have shown persuasively how PCTs are co‐constructed within particular healthcare systems in which they are based, they have tended to focus on relatively later stages in careers of trials. The paper contributes to literature by considering how the ‘real world’ of the UK National Health Service (NHS) is incorporated into the design of a research protocol. Drawing on a meeting held just prior to patient recruitment for a PCT in maternal health, the paper analyses a trial collective's efforts to purify the messy domain of NHS clinical care into the orderly confines of the protocol (Law 2004), which meant satisfying demands for both scientific and social robustness (c.f. Nowotny et al. 2001). The findings show how efforts to inscribe robustness into the PCT protocol were themselves mediated through epistemic and regulatory conventions surrounding protocols as devices in healthcare research. Finally it is argued that meetings constitute an important epistemic instrument through which to settle various emerging tensions in PCT protocol design.