In this paper, we draw on the analytic perspectives of ethnomethodology to explore doctor-patient encounters in an experimental trial of a complex intervention: an efficacy randomised controlled trial (RCT) of decision-support tools in the UK. We show how the experimental context in which these encounters take place pervades the interactions within them. We argue that two interactional orders were at work in the encounters that we observed: (i) the ceremonial order of the consultation and (ii) the assemblage of the decision-support tool trial. We demonstrate how doctors in the trial oscillate between positions as authoritative clinician and neutralistic decision-support tool-implementer, and patients move between positions as passive recipients of clinical knowledge and as active subjects required to render their experience as calculable in terms of the demands of the decision-support tools and the broader trial they are embedded in. We demonstrate how the RCT coordinates the world of the clinical environment and the world of experimental evidence.