Background: The movement towards research and evidence-based practice in health care demands that the best available evidence is applied to practice. At the same time, changes to role boundaries mean that nurses are assuming increased responsibility, especially in relation to decision making. While increasing, there has been limited consideration about the application of best evidence and decision making by nurses in the context of their clinical work. Objectives: This study sought to explore the realities of research and evidence-based practice through an examination of the decision making of nurses when extubating patients following cardiac surgery. Design: The tradition of qualitative research and, more specifically, ethnography were used for the study. Setting: Data were gathered over an 18-month period during 1998 and 1999 within a Cardiothoracic Intensive Care Unit (CICU). Participants: The sample comprised 43 nursing, 16 medical and two managerial staff. A purposive sample of five nurses, a cardiac surgeon, intensivist, CICU manager and Deputy Divisional Manager were included in interviews. Methods: All staff were included in participant observation. Semi-structured interviews were conducted with a purposive sample of nurses during the 6th and 14th months and with a purposive sample of other staff during the 16th month. Data were analysed using progressive focusing, data source triangulation and sensitising concepts to identify themes and categories. Results: The findings indicated that, despite the use of an unwritten physiologically based protocol for weaning and extubation, factors other than best evidence were significant in nurses' decision making. A range of personal, cultural and contextual factors including relationships, hierarchy, power, leadership, education, experience and responsibility influenced their decision making. Conclusion: This study revealed, often disregarded, cultural, contextual and personal characteristics which combined to form a complex process of decision making. Providing new insight into research and evidence-based practice, the findings have implications for policy makers, educators, managers and clinicians and for the continued professional development of nursing.