United States Army Medical Research Institute of Infectious Diseases

The United States Army Medical Research Institute of Infectious Diseases (USAMRIID; /juːˈsæmrɪd/) is the United States Army's main institution and facility for defensive research into countermeasures against biological warfare. It is located on Fort Detrick, Maryland, near Washington, D.C., and is a subordinate lab of the United States Army Medical Research and Development Command (USAMRDC), headquartered on the same installation.

USAMRIID is the only laboratory of the United States Department of Defense (DoD) equipped to study highly hazardous viruses at Biosafety Level 4 within positive pressure personnel suits.

USAMRIID employs both military and civilian scientists as well as highly specialized support personnel, totaling around 800 people. In the 1950s and 1960s, USAMRIID and its predecessor unit pioneered unique, state-of-the-art biocontainment facilities which it continues to maintain and upgrade. Investigators at its facilities frequently collaborate with the Centers for Disease Control and Prevention, the World Health Organization, and major biomedical and academic centers worldwide.

USAMRIID was the first bio-facility of its type to research the Ames strain of anthrax, determined through genetic analysis to be the bacterium used in the 2001 anthrax attacks.