Throughout scientific work and research,many processes and procedures are maderoutine, mundane and then taken forgranted. So are some underlying assump-tions – not only about the state of the nat-ural world, but about what its different ac-tors are supposed or expected to be orwork like. These assumptions are not onlydescriptive, but prescriptive. If we pro-ceed from the notion that expectations andbeliefs are written into our everyday prac-tices and made opaque even to their prac-titioners, it becomes an urgent issue tofind tools to better scrutinize and evaluatethem. This is, I argue, a matter of ethics.How such assumptions are written intopractices is perhaps as available as ever, inthe instructions, documents and processesof evidence-based science. When somepremises and practices are locked to eachother, others are excluded. The aim of thisarticle is to explore the dynamics of thisprocess in a biomedical research practice,with regard to how it affects what are con-sidered ethical issues and how they arehandled.Based on ethnographic fieldwork, I willinvestigate what happened when staff in alarge-scale and multi-site cell transplanta-tion trial in Parkinson’s research had toscrutinize their procedures. I want to un-derstand what subsequent negotiationsneeded to be done in order to progress; or,more specifically, what deliberationsabout perspectives, procedures and ethicalissues of the project were required to seethe trial through. The focus is on what thestaff described as causing the major delaysthat they faced, and temporality is subse-quently conceptualized as an importantfactor in the homogenization and repro-ducibility of science. I discuss how thenecessary changes and negotiations relateto the aims and standards presented by therationale of evidence-based science, andthe implications they have for researchpractice of future trials and for researchethics.I argue that investigations such as thisare crucial to better understand how ethi-cal dilemmas are not primarily abstractdeliberations addressed in policy docu-ments, but embedded in everyday prac-tice. I will also address the importance ofethnographic practices to this end.In the following, the content and theconditions of the trial will be presented incontext.