Objectives: To understand the extent to which the assistant practitioner role is described as `assistive' in formal job descriptions and analyse whether the term `assistive' has been stretched to encompass more `substitutive' or `autonomous' characteristics. Methods: Sixteen AP job descriptions representing all clinical divisions across one UK acute NHS Hospital Trust were both macro- and micro-analysed for broad similarities and differences in line with Hammersley and Atkinson's analytical framework. The analysis specifically focused on how clinical tasks were related to clinical responsibility, from this the job descriptors were then indexed as belonging to one of five discrete categories. Results: Our analysis revealed the following categories: fully assistive (n = 1), supportive/assistive (n = 7), supportive/substitutive (n = 4), substitutive/autonomous (n = 3) and fully autonomous (n = 1). From this, a number of anomalies manifest in the form of divergent organisational expectations regarding the AP role. Conclusions: This study highlights a series of tensions extant between policy vision and implementation of the AP role in practice. Introduction of new healthcare roles requires compromise and negotiation, to shape and define what social space incumbents of these and existing roles will occupy. However the way in which new roles are defined will determine how they become embraced and embedded within future healthcare services. (C) 2008 Elsevier Ireland Ltd. All rights reserved.