The structure and content of written forms of communication dynamically interact with the social and historical conditions underlying critical care nursing activities. One important form of documentation regularly used in the critical care area is the medication order chart. This paper considers the ways in which medication order charts are used to structure interactions among nurses and between nurses and doctors. The critical ethnographic study upon which this paper is based involved a research group of six nurses who worked in one critical care unit. Data collection methods involved professional journalling, participant observation and individual and focus group interviews. Data analysis identified four major issues for consideration: imbalance between medical knowledge and legal authority; the nurse as go-between and medication expert; coaching the doctor; and the self policing nurse. The critical care nurse's role extends beyond the traditional passive activity of medication administration. By exploring the power relations underlying this role, there is greater opportunity for improved nursing relationships and patient care.