The manner in which clinical and cost-effectiveness data are used to inform decisions about the funding and availability of drugs, therapies and medical devices is inherently politicised within collectively financed systems of health care. The National Institute for Health and Clinical Excellence (NICE) was established by the British government in 1999 to reach evidence-based decisions on whether selected health technologies should be made available by the National Health Service in England and Wales. But NICE is also required to involve a broad range of interested parties in the decision-making process, provide detailed rationales for its rulings and defend appeals from aggrieved parties. Debates about the emergence of "deliberative" forms of policy governance--based upon participation by a broad range of stakeholders rather than reliance on scientific, bureaucratic or political expertise alone--are thus particularly apposite. This article draws on a study of decision-making within NICE by focusing upon the tenor and orientation of deliberation about the adoption of health technologies. Does such deliberation take place upon a level playing field for different interests? Or do implicit parameters and understandings in the deliberative process tend to privilege some interests by structuring debate and attendant outcomes? Findings suggest that deliberative assumptions and parameters pertaining to fluid and contestable ideas of transparent reasoning and domain competence both reflect and shape relationships of influence and marginality among participants. Broader analytical implications centre on a distinction between "deliberative democracy" and "democratic deliberation". The extent to which this distinction is acknowledged and addressed in policy and practise will have marked implications for the substantive nature of attempts to broaden involvement in decision-making within public sector bodies such as NICE.