This article critically analyses biological citizenship in terms of how it instates an ideal human subject drawn expressly from Western liberal discourse. Through an analysis of health promotion booklets directed at people living with HIV in South Africa, it reveals how regimes of biological citizenship valorise individual responsibility, agency and rationality, all attributes of the human imagined by liberal humanism. Drawing on insights from posthumanist scholarship, I argue that perceived failure to perform these attributes can operate to disqualify certain marginalised HIV-positive subjects from full citizenship. Far from immaterial, attributions of citizenship have material implications for access to human rights, including the right to life-saving treatment. Importantly, they also shape HIV/AIDS, producing two qualitatively different ontologies of disease: (i) a chronic, manageable illness for those who qualify as citizens; and (ii) a life-threatening, debilitating one for those denied full citizenship and who therefore cannot access the rights and rewards attendant on it.