Kenyan duo Dickson Chumba and Florence Kiplagat will be looking to defend their Chicago Marathon crowns on Sunday.
Chumba beat Sammy Kitwara to first position in Illinois last year, and he will be the fastest male in the field this time around following the withdrawal of world record holder Dennis Kimetto due to injury.
Chumba, who finished third at this year's Tokyo Marathon, clearly enjoys running in Chicago as his personal best of two hours, four minutes and 32 seconds was set here in 2014 when he finished third.
However, he will face stiff competition from Ethiopia's Tsegaye Kebede, a bronze medallist at Beijing 2008 who also has pedigree in the American city.
Kebede was the 2012 champion in Chicago, securing the win with a personal best that is just six seconds slower than Chumba's.
But two-time world champion Abel Kirui, Micah Kogo and Gideon Kipketer will also be in the hunt.
In the women's event, Kiplagat will be aiming to become the first woman to win successive titles since Ethiopia's Berhane Adere triumphed in 2006 and 2007.
Kiplagat broke away from Ethiopian duo Yebrgual Melese, who was a late addition to this year's field and will be out to improve upon her runner-up spot last time out, and Birhane Dibabe to take the win in 2015.
Along with the Kenyan, who placed third in London earlier this year, only one other competitor has produced a time below two hours and 20 minutes - Edna Kiplagat.
The two-time world champion earned a place on the podium in Tokyo in February and will be hoping to improve in Chicago.
Ethiopia's Atsede Baysa cannot be discounted either, having triumphed here in 2010 and 2012 and also winning the Boston Marathon in April.