Kenya's Dennis Kimetto and Ethiopia's Tirunesh Dibaba are among the runners to beat in Sunday's Chicago Marathon, where Kenya's Florence Kiplagat seeks her third consecutive Chicago crown.
Dibaba, who owns the world 5,000m record of 14:11.15, will be tested by Kiplagat, who won last year in 2:21:32, nearly two minutes ahead of runner-up Edna Kiplagat.
Kimetto, 33, is the world record-holder over the 26.2 miles from his 2014 Berlin triumph in 2:02:57. He also won at Chicago and Tokyo in 2013, capturing the US race in 2:03:45.
But Kimetto is a bit of a mystery this time around, having failed to finish two of his four marathon starts since 2014, including this year's Boston Marathon in April due to an injury.
Kenya's Stanley Biwott, the 2015 New York Marathon winner, was second at London last year in 2:03:51, making him second-fastest in the field Sunday in his Chicago debut.
And Olympic runner-up Feyisa Lilesa of Ethiopia, last year's Tokyo Marathon winner, comes to Chicago off a New York Half Marathon triumph. He was third at Chicago in 2010 and second in 2012.
The defending Chicago champion is Kenya's 35-year-old Abel Kirui, the 2012 London Olympic marathon runner-up who captured world marathon titles in 2009 and 2011 and edged Dickson Chumba by three seconds last year in 2:11:23. Kirui was fourth at this year's London Marathon.
Ethiopia's Zersenay Tadese, 35, was eighth in the 10,000m in Rio and is hoping to complete a marathon for the fourth time in his career.
Dibaba, 32, is a two-time 5,000m world champion and three-time 10,000m world champion who settled for second at this year's worlds in London, trailing only compatriot Almaz Ayana.
Dibaba won 5,000 and 10,000 gold at the 2008 Beijing Olympics and defended the longer crown four years later in London. Last year in Rio, Dibaba was third in the 10,000 with the fourth-fastest time in history.
Now she is chasing the Chicago Marathon women's course record of 2:17:18 set by Britain's world-record holder Paula Radcliffe in 2002. And Dibaba won at London in April in 2:17:56, becoming the third-fastest woman at the distance on a similar flat course.
"I've always been building to marathons," Dibaba said. "I want to use my 10k foot speed and make history.