Background: Since 1995, UK cancer policy has been directed at organizational changes to secure improvements in treatment outcomes and quality of supportive care for cancer patients. The substantial increase in hospital-based specialist cancer nurses (SCNs) during this time suggests they have a major role to play in the delivery of supportive care. Aim: To explore how SCNs implemented their role in the context of organizational change and newly-formed multidisciplinary teams. Methods: Twenty-nine SCNs participated in observation and/or interviews, resulting in 135 hours of observation and in-depth semi-structured interviews with 17 SCNs. Data were collected and analysed using a grounded theory approach. Results: The prominence of the treatment agenda - the process of investigating, diagnosing and treating cancer - presented the biggest challenge to the delivery of supportive care. The treatment agenda influenced how support was offered, determined professional boundaries and relegated support to a subordinate position in patient care. Conclusions: Access to supportive care is a central tenet of current cancer policy and crucial to the philosophy of patient-centred care. While SCNs are essential to the delivery of supportive care, this study highlights the challenges they encounter in organizations which prioritise treatment and improvements to treatment outcomes. © 2005 Edward Arnold (Publishers) Ltd.