We present findings from evaluations of two government-funded initiatives exploring the transfer of research evidence into clinical practice--the PACE Programme (Promoting Action on Clinical Effectiveness), and the Welsh Clinical Effectiveness Initiative National Demonstration Projects. We situate the findings within the context of available research evidence from healthcare and other settings on the role of opinion leaders or product champions in innovation and change--evidence which leaves a number of problems and unanswered questions. A major concern is the difficulty of achieving a single replicable description of what opinion leaders are and what they do--subjective understandings of their role differ from one setting to another, and we identify a range of very different types of opinion leadership. What makes someone a credible and influential authority is derived not just from their own personality and skills and the dynamic of their relationship with other individuals, but also from other context-specific factors. We examine the question of expert versus peer opinion leaders, and the potential for these different categories to be more or less influential at different stages in the innovation process. An often neglected area is the impact of opinion leaders who are ambivalent or hostile to an innovation. Finally, we note that the interaction between individual opinion leaders and the collective process of negotiating a change and reorienting professional norms remains poorly understood. This raises a number of methodological concerns which need to be considered in further research in this area.