Federal and military officials are investigating a hazmat incident that sickened 11 Marines at Joint Base Myer-Henderson Hall in Arlington, Virginia, on Tuesday.
The FBI and the Naval Criminal Investigative Service were called in when the Marine Corps personnel began feeling ill after an envelope containing an unknown substance was opened at the joint base, which is next to Arlington National Cemetery and near the Pentagon.
Personnel inside the building were immediately evacuated, officials said, and local fire department hazmat teams responded to the scene within minutes.
Three Marines were transported to a nearby hospital for treatment with non-life threatening conditions. They were treated and released from the hospital late Tuesday night, according to a press release from Joint Base Myer-Henderson Hall.
The eight others, who had symptoms ranging from itching to nasal irritation, were being assessed, a Marine official told ABC News.
Field tests on the suspicious material found inside the envelope came back negative for any known substance, a law enforcement official told ABC News. The envelope and the substance were taken to the FBI's lab at Quantico for further testing.
The incident remains under investigation. The FBI and the NCIS are conducting a joint investigation, according to the press release from Joint Base Myer-Henderson Hall.
Joint Base Myer-Henderson Hall is the name for the Army and Marine base commonly-known as Fort Myer, home to the Old Guard honor guard unit and Henderson Hall, where Marines are stationed.
ABC News' Mark Osborne and Morgan Winsor contributed to this report.