Two of the four fastest men in history, American sprinter Tyson Gay and Jamaica's Asafa Powell, have sent shockwaves through the athletics world after failing drug tests.
Gay, who was the 100 metres and 200 metres world champion in 2007 and the fastest man in the world this year, tested positive and has withdrawn from next month's world championships in Moscow.
Powell, a former 100 metres world record holder, has confirmed he also tested positive positive for a banned stimulant at Jamaica's recent national trials for Moscow, but denies any wrongdoing.
Gay insists he's never knowingly taken a performance-enhancing drug, he basically put his trust in someone and was let down - but he says he can't divulge the substance nor how the positive result came about.
The US Anti-Doping agency has released a statement applauding Gay for voluntarily removing himself from competition while the full facts surrounding his test are evaluated.