Chapter five analyses the expansion of environmental protest after Chernobyl in 1986. The environmental movement became more public in eastern Europe in general, and the GDR in particular. Bolstered by western support, unrest grew swiftly in an uncertain political context. The chapter explores East German reactions to Chernobyl and new challenges for the movement. The Stasi’s efforts to sow discord among uneasily allied environmentalists succeeded in curbing their potential impact. Yet the relative openness in Poland permitted outrage over Chernobyl and further fueled discussion of other environmental problems, making it an ideal location for exchange across borders within the region. Finally, the chapter turns to deepened West German interactions with eastern European pollution and protest, teasing out moments of cooperation and misunderstanding. Responses to Chernobyl reshaped environmental movements, anti-communist rhetoric, and connections. Nevertheless, the nuclear disaster and its fallout undermined a system that was already on shaky ground.