This article looks at HIV prevention projects in which established stigmatized and stigmatizing roles were actively reversed and manipulated in pursuit of HIV harm reduction. In two Norwegian projects, sex workers and drug users carried out harm-reduction activities with other drug users and sex workers. Although HIV-related harm reduction was the aim of the projects, termination or reduction of drug use or sex work was not. Such changes nevertheless occurred among the sex workers and drug users who took active part in the project. The article considers these changes in order to reflect on the meanings and roles of participation in HIV prevention work. In particular, the discussion theorizes on possible ways in which alteration of roles and subject positions may produce self-reflective effects with transformative potentials.