Dallas Fire-Rescue was called to 1555 Regal Row Thursday morning where two people were exposed to a letter containing a white powder.
Jason Evans, with DFR, said two employees at Allied Marketing were exposed to the powder, but showed no symptoms of being exposed to anything toxic.
Plano's Hazardous Materials Team responded to the scene and tested the powder -- all of which came back negative for a hazardous substance.
The case is being turned over to the FBI's Dallas office.
Letters containing powder invoke fear after five people were killed and more than a dozen were injured when letters laced with anthrax spores were mailed to offices in the days and weeks after Sept. 11, 2001.
Since then, hundreds of hoax letters have been received nationwide at schools, banks, hospitals and other businesses. Though they've been harmless, anyone receiving a white powder letter is advised to evacuate the area and call 911.