In the transition out of socialism to market capitalism, bodies, populations, and categories of citizenship have been reordered. The rational-technical management of groups affected by the Chernobyl disaster in Ukraine is a window into this contested process. Chernobyl exemplifies a moment when scientific knowability collapsed and new maps and categories of entitlement emerged. Older models of welfare rely on precise definitions situating citizens and their attributes on a cross-mesh of known categories upon which claims rights are based. Here one observes how ambiguities related to categorizing suffering created a political field in which a state, forms of citizenship, and informal economies were remade.