Paula Radcliffe pulled out of the Olympic marathon at the 36km mark as the scorching heat and humidity left her exhausted and unable to carry on.
The British world record holder and favourite to win was leading for the first 15km, but then slipped to fourth and stopped, looking very distressed.
She bravely tried to restart, but stopped again and finally gave up.
The race was eventually won by Japan's Mizuki Noguchi who took the gold in two hours 26 minutes and 20 seconds.
Kenyan Catherine Ndereba took silver, and America's Deena Kastor clinched bronze.
Radcliffe, who skipped this year's London marathon to concentrate on Olympic training, finished just seven kilometres from the end, and sat slumped on the side of the road with her head in her hands.