Chronology of major doping incidents in world sport:
Chambers is banned for two years and Britain stripped of their world 4x100 relay silver medals.
Chambers' coach Remi Korchemny and Victor Conte, owner of Californian laboratory BALCO, among four men indicted by US federal grand jury on charges of distributing illegal steroids and human growth hormones. All four plead not guilty.
May: Double world sprint champion Kelli White, also coached by Korchemny, becomes the first athlete to be banned for a "non-analytical positive". Under World Anti-Doping Agency rules, athletes can be banned if there is sufficient evidence of doping other than a positive test.
June: World 100 metres record holder Tim Montgomery, Jones's new partner, receives a letter from the US Anti-Doping Agency alleging doping violations.
July: Three riders, including Britain's David Millar, are not allowed to start the Tour de France. Two others are kicked out after the Tour begins because of doping investigations.
Millar later admits to taking the blood booster EPO (erythropoietin).
August: Torri Edwards, awarded the world championships 100 metres gold medal after White's disqualification, is banned for two years after a positive test for a stimulant.
Greece's 200 metres Sydney champion Costas Kenteris and compatriot Katerina Thanou, the 100 metres women's silver medallist in 2000, fail to attend drugs tests on eve of opening of Games and are summoned to IOC disciplinary hearing.
Scientists at the Olympic Analytical Laboratory in Los Angeles discover a new designer steroid THG after an anonymous tipoff from a man, rumoured to be a well-known athletics coach.
Britain's European 100 metres champion Dwain Chambers is one of five track and field athletes to test positive for THG.
World shot put champion CJ Hunter tests positive four times for excessive levels of nandrolone. The results are announced during the Sydney Olympics where his wife Marion Jones wins three gold medals.
Festina rider Richard Virenque of France is banned for six months after admitting doping.
Britain's 1992 Olympic 100 metres champion Linford Christie is suspended after positive test for nandrolone.
January: Chinese swimmer Yuan Yuan and her coach are banned from the Perth, Australia, world championships after 13 vials of human growth hormone are found in the swimmers' bags at airport.
Four more Chinese are suspended after testing positive for a banned diuretic.
July: Festina cycling team expelled in the first week of the Tour de France after customs officers discover a team car loaded with performance-enhancing drugs.
Team director Bruno Roussel admits to widespread doping.
Seven swimmers are among 11 Chinese competitors who test positive for steroids at the Asian Games in Hiroshima. China lose nine of their 23 gold medals.
Canadian government sets up official inquiry under Charles Dubin, an associate chief justice of the Ontario Supreme Court.
Johnson's coach Charlie Francis and his doctor Jamie Astaphan tell the inquiry Johnson had been taking steroids since 1981. Johnson admits taking steroids and lying.
World governing body strips Johnson of all his marks, including world record 9.83 seconds set in 1987 in Rome.
Canadian sprinter Ben Johnson tests positive for the anabolic steroid stanozolol after winning the Seoul Olympic 100 metres final in a world-record 9.79 seconds.
Johnson, who denies ever taking a performance-enhancing drug, is stripped of his gold medal which is awarded to second-placed American Carl Lewis, the defending champion.
Briton Tommy Simpson dies on a hill climb during the Tour de France. A vial containing an amphetamine is found on his body.
In cycling, Danish rider Knut Jensen dies at the Rome Olympics after taking nicotinic acid and amphetamines.