Samples taken from this season's Grand Slams, Davis and Fed Cup are to be re-tested for the newly discovered steroid tetrahydrogestrinone (THG).
The testing process has only recently been able to detect THG. Four US athletes along with British sprinter Dwain Chambers have already tested positive.
Under the ITF's anti-doping policy everyone in a Davis Cup or Fed Cup squad must be tested. Players tested at Grand Slam events are selected randomly.
International Tennis Federation president Francesco Ricci Bitti said: "We have just decided to have a number of retroactive tests for THG. Fighting against doping is a must for us, for the health of young people and for the integrity of the sport."
Filed by Mark O'Neill-Cummins
