Two customs inspectors became sick after inhaling fumes from a package at New York's John F. Kennedy International Airport on Sunday morning, according to local media reports.
FBI HAZMAT and Port Authority police are investigating the incident at the U.S. Postal Service facility.
The item initially tested positive for VX, one of the most potent chemical weapon known to man.
Law enforcement officials, however, said the test result appeared to be a false positive. Authorities believe package contained a solvent or degreaser that shouldn't have been in the mail.
Both victims suffered respiratory distress and received emergency treatment. They quickly recovered and declined further medical care.
Authorities said the package may have arrived from China.