In this talk, I build on the critical framework of “local biologies” to examine how two chemicals are woven into the infrastructure of global health, and into the social lives of health workers in urban Nicaragua. One chemical is temephos, an organophosphate insecticide used to control the mosquitoes that transmit the dengue virus. The other is chlorine (mostly in the form of diluted bleach) used to disinfect surfaces and purify water. For global health, both temephos and chlorine are useful killers. They end the lives of mosquitoes and microbes in order to preserve those of humans. Chemicals are key material features of the infrastructure of global health. While the models for disease control deployed in global health projects tend to treat chemicals as stable objects, I draw on critical studies of other public technologies to argue for a view of chemicals as leaky things, implicated in fluid sociomaterial interactions. My ethnographic work reveals three kinds of leakages in global health’s chemical infrastructure. First, global health chemicals are tracked through rigid bureaucratic accounting, but in due to numerical leakages, they become vehicles for fashioning new forms of concern. Second, like other global technologies, tempers and chlorine leak structurally. They can be broken down and reproduced at a molecular level, though that breakdown is never absolute, and that reproduction is not always and everywhere the same. Third, chemicals reveal the importance of sensory leakages to global health. Sensory interactions with chemicals produce an entanglement of knowledge about bodies and knowledge about urban environments.