The furore over the discovery of THG has intensified after Dwain Chambers' coach Remi Korchemny, was among four men indicted by a federal grand jury in America on charges relating to distributing steroids to athletes.
Chambers has now been banned for two years by UK Athletics after testing positive for THG.
What is THG, and why does it matter?
Tetrahydrogestrinone is a banned steroid which had been tweaked by chemists to make it undetectable by normal dope tests.
What will happen after the indictments?
The four involved will see their cases come to court - and more names could follow, although no charges were expected to be brought against actual athletes for now.
The IAAF has announced plans to re-test all the samples given at the 2003 World Championships while the International Olympic Committee may do the same with samples from the 2002 Winter Games in Salt Lake City.
Why is this such a big story?
Athletics was the first sport to be hit by the controversy but now the net is widening.
The THG scandal could be as big as the Ben Johnson case
If found guilty of doping, any sportsman or woman who won medals at either the 2003 World Athletics Championships or the 2002 Winter Olympics could have them taken away and their performances scratched from the record books.
Add to this the fact that THG is designed to evade existing drug tests, you have the ingredients for a drugs story to rival the Ben Johnson scandal at the 1988 Olympics.
How did the story break?
The United States Anti-Doping Agency was contacted by an anonymous athletics coach who claimed that several top athletes were using THG.
The same coach then handed over a syringe containing THG, which USADA used to develop an effective test for the substance.
Urine samples taken at the US championships were then re-tested, resulting in a number of positive tests.
Why would an athlete take THG?
Anabolic steroids can improve the body's capacity to train and compete at the highest level. They reduce the fatigue associated with training and the time required to recover after physical exertion.
They also promote the development of muscle tissue in the body, with an associated increase in strength and power.
What is Balco?
Balco is the Bay Area Laboratory Cooperative, a company which makes nutritional supplements. It has been identified by the United States Anti-Doping Agency as the source of THG.
The company analyses blood and urine from athletes and then prescribes a series of supplements to compensate for vitamin and mineral deficiencies.
Among its clients are top athletes Marion Jones and Tim Montgomery, as well as baseball star Barry Bonds and the NFL's Bill Romanowski.
Bonds has been a Balco client since the winter of 2000 and has credited the company for a personalised programme that includes nutritional supplements.
Why was a federal grand jury investigating Balco?
For alleged tax evasion.
Why were Jones and Montgomery called to give evidence?
They were listed as clients of Balco but are not the focus of the probe. The grand jury wanted to question them - and the other 39 sportsmen subpoenaed - about financial relationships with Balco's president, Victor Conte.
Who is Victor Conte?
He is the founder of Balco. A former bass player with soul group Tower of Power and jazz pianist Herbie Hancock, he founded Balco in the early 1980s.
One of the bands in which he played was called Pure Food and Drug Act.
How else is Conte linked to Marion Jones?
When Jones' former husband, shot putter CJ Hunter, was found to have 1,000 times the
allowable amount of the steroid nandrolone in his system and was banned by the IAAF prior to the last Olympics, Conte took the blame.
He said the positive test was the result of contaminated iron supplements he had supplied to
What connection does Kelli White have with Balco?
White, the world 100m and 200m champion, tested positive for banned stimulant modafinil at the World Championships in Paris in August.
Kelli White has been called before a US grand jury
White claims to have taken modafinil to combat the sleep disorder narcolepsy. She was prescribed it by Dr Brian Goldman, a psychiatrist who has worked with Balco president Conte for almost 20 years.
Reviews of earlier urine samples revealed that White tested positive for the same drug at the US Championships in June. She was also called to give evidence before the grand jury.