Abel Kirui and Florence Kiplagat will each be hoping for successful title defences when the Chicago Marathon takes place tomorrow.
It will mark the fourth stop on the World Marathon Majors Series circuit which began in London earlier this year.
The Kenyan duo will each have to defeat faster rivals, though, if they are to secure back-to-back triumphs.
In the men's race, world record holder Dennis Kimetto will seek to match the 2 hour 3min 45sec course record he clocked to win in 2013.
His form since his 2:02.57 world record the following year in Berlin has been far less impressive, however, and he has failed to finish two of his four starts over the last three years.
Kirui won last year's race in 2:11:23 but is yet to return to the form which saw him crowned world champion in 2009 and 2011.
Other Kenya challengers are Stanley Biwott, the winner of the 2015 New York City Marathon, while Ethiopia will be led by Olympic silver medallist Feyisa Lilesa.
Olympic bronze medallist Galen Rupp will lead the home challenge as he seeks to improve on his modest personal best of 2:09.58.
Eritrea's 2007 world cross-country champion Zersenay Tadese is another outside contender.
Ethiopia's three-time Olympic track champion Tirunesh Dibaba appears the major challenge for Kiplagat in the women's race.
She clocked 2:17.56 to place second in London earlier this year, making her the third fastest of all time, before returning to the track to take a 10,000 metres world silver medal in the British capital.
Kiplagat won by almost two minutes last year in 2:21.32 and she will be hoping that all her experience and course nous will prove useful again.
Kenyan pair Valentine Kipketer and Bridgid Kosgei are other contenders as well as American rising star Jordan Hasay.
It comes in a race taking place amid tightened security following last week's mass shooting in Las Vegas.
Undercover offices and more fencing along the side of the course are among methods being used.