Unprocessed archival collections can contain unknown and potentially hazardous materials that can be harmful to other collections and staff. Archival literature largely focuses on collection and personnel dangers posed by environmental hazards such as mold and insect infestation but not on pharmaceutical and chemical hazards. In this article, the author reviews her institution's surprise experience with a radioactive discovery and discusses how institutions can proactively prepare for a hazardous materials discovery. The discussion includes identification of threats, drafting of a hazardous materials portion of an institutional disaster plan, making appraisal and processing decisions, and taking action to contain a hazard. (Contains 21 notes.)