Seven people were taken from O'Hare International Airport to nearby hospitals after reporting that they felt sick, officials said.
The Chicago Fire Department responded to a gate at O'Hare about 11 p.m. Monday, said Fire Chief Juan Hernandez.
"People were feeling nauseated, but they weren't boarding or anything like that," Hernandez said.
It was unclear whether those feeling ill were employees or travelers, Hernandez said.
Six people were taken to Resurrection Medical Center in Chicago. Another person was taken to Advocate Lutheran General Hospital in Park Ridge.
All were in stable condition. The cause of the situation was still under investigation, Hernandez said.