In this paper we bring together ethnographic research carried out during two clinical prevention trials to explore identities, relations and political imaginations that were brought to life by these different technologies. We highlight the ways in which critical anthropological engagement in clinical trials can help us radically reconsider the parameters and standards of medical research. In the paper we analyse the very different circumstances that made these two trials possible, highlighting the different temporalities and politics of HIV and Ebola as epidemics. We then describe four themes revealed by ethnographic research with participants and their communities but mediated by the specific sociopolitical contexts in which the trials were taking place. In both countries we found materiality and notions of exchange to be important to participants' understanding of the value of medical research and their role within it. These dynamics were governed through social relations and moral economies that also underpinned challenges to Western notions of research ethics. The clinical trials offered a language to express both disaffection and disillusionment with the political status quo (often through rumours and anxieties) while at the same time setting the foundations for alternative visions of citizenship. Attached to these were expressions of 'uncertainty and hope' steeped in locally distinctive notions of destiny and expectations of the future.