Contemporary developments in health care have encouraged a review of the professional status of psychiatric nursing. However, little study has been made, to date, of the discrete 'need' for psychiatric nursing within a multidisciplinary service. Employing an adapted grounded theory methodology, substantive theory was developed concerning the expressed need for psychiatric nursing, by patients, their carers and mental health professionals, based on six sites from England, Eire and Northern Ireland. The study found some consensus across both recipients and providers of mental health care, that the essential feature of nursing (the core category) involved a complex of relationships: 'knowing you--knowing me'. Within that complex, nurses either elected, or were required, to move--or 'toggle'--between three discrete domains of relating: the Ordinary Me (OM); the Pseudo-ordinary or Engineered Me (POEM); and the Professional Me (PM). Four internal dimensions involving the nurses' depth of knowing, power, use of time and use of translation, distinguished these domains. The emergent theory is discussed within the context of the emergent growth in user (consumer) influence and health care technology.