If nature is to matter, we need more potent, more complex understandings of materiality. New conceptions of materiality, which are neither biologically reductive nor strictly social constructionist, are emerging in science studies, environmental philosophy, corporeal feminism, disability studies and other fields. This essay analyzes scientific, popular and autobiographical accounts of multiple chemical sensitivity (MCS), or environmental illness, arguing that this condition provokes new models of material agency as well as new forms of environmentalism. The material agency of MCS epitomizes “trans-corporeality”—the recognition that the substance of the human is co-extensive with the emergent, more-than-human world.