This paper presents findings from an investigation into requirements for collaboration in e-Science in the context of eDiaMoND, a Grid-enabled prototype system intended in part to support breast cancer screening. Detailed studies based on ethnographic fieldwork reveal the importance of accountability and visibility of work for trust and for the various forms of ‘practical ethical action’ in which clinicians are seen to routinely engage in this setting. We discuss the implications of our findings, specifically for the prospect of using distributed screening to make more effective use of scarce clinical skills and, more generally, for realising the Grid’s potential for sharing data within and across institutions. Understanding how to afford trust and to provide adequate support for ethical concerns relating to the handling of sensitive data is a particular challenge for e-Health systems and for e-Science in general. Future e-Health and e-Science systems will need to be compatible with the ways in which trust is achieved, and practical ethical actions are realised and embedded within work practices.