Emergency officials were called to Stampede Meat Inc. in Bridgeview early Tuesday morning after a chemical spill.
Four workers were taken from the company, at 7351 S. 78th Ave., to area hospitals after complaining they felt sick.
It's unknown what chemicals were mixed together causing the employees to feel ill.
Authorities evacuated the plant and closed streets around the area as a precaution. The streets reopened about 4 1/2 hours later.
A couple hundred employees were in the building at the time.
No residents in the area were affected.
According the company's website, Stampede Meat Inc. is the newest and largest steak cutting facility in the Chicago area. The business specializes in custom-made beef and pork dishes for the restaurant and hospitality industry.