Rockford's one of 15 cities that will participate in the biohazard detection system.
The system uses rapid DNA testing to detect germs. Results are reported immediately, allowing for a quick emergency response.
It was developed in the wake of the anthrax-by-mail attacks in the fall of 2001. Those attacks killed five people.
Officials say the sites were chosen for the four-week test because they represent a range of climates and environments. Pending results of the test, the detection system is expected to be extended to other mail processing centers beginning next year.