Civilian workers at Army Reserve Command headquarters found a bag containing white powder, and initial field tests indicated anthrax, officials said.
The Centers for Disease Control and Prevention was conducting further tests. Security on the post in suburban Atlanta was increased and the building was locked down for five hours, but the 200 people inside were later allowed to leave.
The five civilians who found the packet and two civilians from the fire department who responded were showered at the fort, said Col. Guy Shields, a fort spokesman.
They were sent to a hospital for further examination.