Heat is expected to be a factor in this year's race.
Memories of the extreme heat, high humidity and miserable running conditions of the marathon in 2007 make runners, marathon organizers and city emergency responders cringe. It was enough to make marathon officials stop the race with much of the field still on the course, miles from finishing.
Temperatures are expected to rise into the 80s on race day again this year, but marathon officials say they're ready.
"The event alert system's been very important. I think education with our participants, training and awareness on race day is very, very valuable," said Carey Pinkowski, race director
Chicago's flat course has the reputation of being fast which draws runners from around the world who want to run their best times. But Runner's World editor and former Boston Marathon champ Amby Burfoot says the heat may alter those plans.
"People come to Chicago knowing it's a fast course, knowing the weather is good and so they want that fast time here but you cannot get it on a warm day," said Burfoot.
The marathon's medical director suggests a common sense approach: make sure you get plenty of fluid but don't overdo it.
"Drink to thirst. Your body has a great sense to tell you what your need is," said Dr. George Chiampas, marathon medical director.
Dr. Chiampas says he's confident they'll have enough fluids no matter how hot it gets. But he also expects conditions for most of the runners should be fine.
"The key thing is to pace yourself appropriately. You run a little slower, you don't heat up as much, you don't sweat as much. You don't overheat and get in trouble," said Burfoot.
The event alert system referred to by Pinkowski is a color coded system to warn the runners of conditions out on the course. They developed the system after the 2007 race. And the very next year they got to a code red later in the race. This year race officials say they expect to start the race in green and hope the humidity stays relatively low so they have to go no further than yellow.