Vaginal microbicides are pharmaceutical products in development that are designed to reduce the sexual transmission of HIV in women. They are commonly known as a `woman-controlled technology' and tool for women's empowerment, and form part of a burgeoning field of clinical research into new biotechnologies for HIV prevention. Little work has critically examined how such research and new technologies are produced, and how they in turn contribute to the construction, maintenance or deconstruction of gender relations. Adopting a Foucauldian understanding of power and discourse, and using theoretical insights from science and technology studies (STS), this research explores the coproduction of gender and technology through the case study of vaginal microbicides. 'T'his account of the relations between science, society and technology draws on empirical research conducted in the UK and Zambia with the pharmaceutical industry, trialists, trial participants and trial communities. It interrogates the techniques of power through which transnational scientific networks are mobilised to test new products, such as microbicides, and how these affect scientific practices, knowledges and identities across socio-geographic boundaries. It attends to the potential multiplicity of interventions in diverse contexts, calling into question the presumed stability and singularity of both the randomized controlled trial and vaginal microbicides. This research makes an empirical contribution to knowledge about new biomedical technologies for HIV prevention, detailing the transformation that may occur when technologies travel from their site of development to their site of use. It provides a detailed analysis of the interaction between gender performativity and science in action, challenging the sense of `gendered' technologies for a `feminized' epidemic. Theoretically, it contributes to debates about the role of social theory in public health research and reconstructivist agendas in STS, concluding with a model for greater collaboration between health technology designers, evaluators, critics, and users.