Background. Expertise in nursing has been widely studied; there have been no previous studies into what constitute expertise in nephrology (renal) nursing. This paper describes a 'real-world' characteristic of expert nephrology nursing practice.Aims and objectives. This paper, which is abstracted from a larger study into the acquisition and exercise of nephrology nursing expertise, aims to explore the concept blurring the boundaries.Design. The study utilized grounded theory methodology and symbolic interactionism.Methods. The study took place in one renal unit in New South Wales. Sampling was purposive then theoretical; the sample consisting of six non-expert and eleven expert nurses. Simultaneous data collection and analysis using participant observation, review of nursing documentation and semi-structured interviews was undertaken.Results. The study revealed that only expert nephrology nurses 'blurred the boundaries' of professional nursing practice. They did this by moving intermittently and purposefully, for the benefit of particular patients, into medical domains in the areas of prescribing, dispensing and ordering of pathology tests. Non-expert nurses did not cross these professional boundaries.Conclusions. Blurring the boundaries was a significant feature of expert nursing practice, and this study was the first to describe explicitly nursing boundaries as two distinct entities; that is, formal and informal.Relevance to clinical practice. There are some nephrology nurses who have sufficient knowledge and experience to prescribe some medications and to order certain investigations.