Wednesday 16 March 2016 09:47, UK
The International Olympic Committee and World Anti-Doping Authority have announced selected samples from the 2008 Beijing and 2012 London Games are being retested.
The tests are targeted at particular athletes and nations, some of whom are expected to be competing in this year's Olympics in Rio.
An IOC statement read: "The reanalysis of hundreds of samples from London 2012 and Beijing 2008 is already under way. The IOC and WADA have together identified and agreed on the sports and countries being targeted.
"This includes in particular athletes likely to compete in Rio de Janeiro who also competed in London and Beijing 2008, and specific methods of analysis where there have been advances during the time since Beijing 2008 and London 2012."
IOC medical and scientific director Richard Budgett said: "The aim of the programme is to prevent athletes who cheated in London or Beijing, and got away with it because we didn't have as advanced methods of analysis as we do now, from competing in Rio de Janeiro. The results will come in a number of weeks or months."
A WADA-run specialist task force has also been established for intelligence-based target testing of athletes throughout the Games.
Budgett added: "We are trying passionately to protect those clean athletes who are going to Rio 2016. And the best way to do that is to catch the cheats and deter the cheats before we get to Rio de Janeiro. So that's why we launched this initiative with the task force even before the Olympic Games open."
