Half of all competitors—and all those who win medals—can expect to be tested for performance enhancing drugs at the London Olympics, the organisers have announced.

A 150 strong team will take more than 6000 samples from Monday 16 July to the end of the games for analysis at a laboratory that will run 24 hours a day, seven days a week.

But do performance enhancing techniques exist that cannot be detected and that may emerge only years later, when somebody admits to having used them to win a medal in London? Leading sports medicine scientists at a media briefing at the Science Media Centre in London on 16 July admitted that there may be.

Among well established methods, autologous blood transfusions can be used by athletes to boost their oxygen carrying capacity by transfusing their own blood, stored earlier, just before competition. The transfusions can be detected by measuring the ratio of mature to immature red cells in the …