This paper addresses the role emotions play in the social assemblage of medicines and technical processes in the response to the HIV called pre-exposure prophylaxis (PrEP) for HIV. We describe a series of stages and processes in the social construction of PrEP in Brazil from the run-up to the launch of the initiative by the Ministry of Health to the subsequent implementation of the strategy by public health services. To understand the meanings and symbolism assigned to this biomedical technology, we examined the hopes underpinning scientific, government and non-governmental narratives, clinical processes and health policy. The social trajectory of PrEP was influenced not only by these hopes but also by fears and concerns about the impact of this approach to HIV prevention on lifestyles and modes of sexual governance. The evidence used in this study comes from interviews with health professionals and AIDS activists, anthropological fieldwork, scientific articles and documentary analysis. Our findings provide important insights into how emotions have shaped the meanings assigned to PrEP and shed light on the complex game of negotiation involved in defining responses to the HIV epidemic.