This paper reflects on a longitudinal collaborative action research programme between the Centre for Research in Strategic Purchasing and Supply and the UK National Health Service Purchasing and Supply Agency that has operated since 1995. During the collaboration, research has changed practice and practice has changed research. A framework for analysing change is introduced as a means of examining how supply strategy has changed during the course of the research. The framework is applied to three supply strategy cases of prosthetics, clinical waste and cardiology, illustrating how practice and research have changed and influenced the production of knowledge over time. The methodological, theoretical and managerial implications of such longitudinal action research programmes are reflected on.