Under the Comprehensive Environmental Response, Compensation, and Liability Act, each year the Agency for Toxic Substances and Disease Registry’s Division of Toxicology (ATSDR) at the Department of Health and Human Services (HHS) publishes in the federal register a list of priority substances for which it may create new toxicological profiles. This year’s list contains 73 proposed substances, one of which is "nanomaterials." The generic use of the term "nanomaterials" without reference to any particular nanoscale material is unusual and most likely unworkable. We’ve asked ASTDR how "nanomaterials" ended up on the list and exactly what it means in this context. Stay tuned.