Montreal police were called to a home in north-end Cartierville on Thursday evening after a woman found a suspicious letter in her mail.
The woman had been the victim of threats in the past which led police to believe the letter might have been hazardous.
Firefighters and investigators set up a perimeter behind a police station and analyzed the letter wearing bio-hazard suits.
No powder or hazardous substance was recovered and there was nothing inside the envelope.
The letter will be sent to the Quebec's public health institute for more tests.
There was no return address on the envelope and police want to determine its origin.
The operation began at 11 p.m. and ended at 3 a.m. Friday.
