Traditionally, surgeons (and to a lesser extent anaesthetists) have been assisted primarily by nurses. This role has been threatened in recent years, in the UK NHS (and elsewhere), by a relatively new profession, that of the Operating Department Practitioner (ODP). The ODP profession is still in the process of establishing itself as a 'full' profession within UK health care. While occupational boundary disputes between professions are common in health care, it is unusual for them to become as overt as the dispute we will analyse in this paper. Drawing on fieldwork observations and interviews conducted in operating theatres, as well as documentary sources, we will show how this dispute arose, how it is manifested at both the micro and the macro level, and how both groups involved justify their positions, drawing on surprisingly similar rhetorical strategies. A further unusual feature of this dispute is the fact that, unlike many attempts by managers to substitute one type of labour for another, issues of cost are relatively unimportant, as both theatre nurses and ODPs earn similar salaries.