Deadly fumes in a house left four young men dead and a woman in critical condition Friday, authorities said.

"It might be either gas or carbon monoxide, but we're leaning toward carbon monoxide - possibly from a defective furnace or chimney," Fire Department spokesman Scott La Greca said.Four men, ranging in age from 17 to 36, were pronounced dead on arrival at Holy Cross Hospital, said supervisor Joyce Kopecky.

A fifth victim, Carol Prykop, 18, was in critical but stable condition at University of Chicago Hospital, said spokeswoman Susan Philips.