Various US agencies, including the Department of Health and Human Services, deemed more than 80 types of bacteria, viruses, fungi, and toxins as "select agents" after Sept. 11, 2001. These hazardous substances, biological and chemical, were chosen for their threat to the health of humans, animals, and plants. The Centers for Disease Control and Prevention (CDC) allowed scientists to comment on the proposed list and made appropriate changes before finalizing it in the fall of 2002. The Public Health Security and Bioterrorism Preparedness and Response Act of 2002 details the regulation and handling of these agents.