Kenya's former triple world cross country champion Edith Masai, 40, has her sights on a medal in the marathon at the 2008 Beijing Olympics and then plans to retire the year after.
"I have seen it all and I think time is up for me," Masai said.
"Cross country no longer excites me, hence my entry into the marathon. I will focus my training on the Games in Beijing where I want to finish among the top three then call it quits the following year."
The Kenyan, who only took up running seriously in 1999 after splitting from her husband, won her debut marathon in Hamburg in 2005.