A chronology of doping problems to hit cycling in recent years:
1998 Tour de France
" Festina medical team member Willy Voet is arrested at the French border before the start of the Tour after customs officers seize banned substances, including the blood-boosting drug erythropoietin (EPO).
" Festina is kicked out of the race and their riders later admit to taking performance-enhancing drugs. Top rider Richard Virenque is banned for nine months, team director Bruno Roussel and Voet are fined and given suspended jail sentences.
1999 Giro d'Italia
" Tour and Giro champion Marco Pantani of Italy is expelled while leading the race after failing a blood test.
2001 Giro d'Italia
" France's Pascal Herve is forced out from the Giro by his Alexia team after failing a test for EPO. Mercatone Uno rider Riccardo Forconi does not start Stage 17 after failing a doping test.
" Police officers search the rooms of riders from all 20 teams, confiscating medicines. Organizers cancel the 18th stage when riders call a meeting to discuss the raids.
" Second-place Dario Frigo is sacked by Fassa Bortolo after illegal drugs are found in his room. Frigo later admits to carrying them as security in case he needed a boost during the final stages of the race.
" An insulin syringe found in a room where Pantani stayed leads to a six-month ban for the Italian. Pantani would later die of a cocaine overdose in 2004.
2002 Giro d'Italia
" Italian Nicola Chesini is arrested by police after Stage 5 as part of a probe into the sale of performance-enhancing drugs.
" Race favorite and 2000 winner Stefano Garzelli tests positive for the banned diuretic and masking agent probenecid and is expelled from the race. He is given a nine-month ban.
" Gilberto Simoni, the 2001 winner, tests positive for cocaine. He withdraws from the Giro but is later cleared by the Italian Cycling Federation.
" Italian Roberto Sgambelluri and Russian Faat Zakirov become the first professional cyclists to be caught using NESP (an improved form of EPO) and quit the Giro.
2002 Tour de France
" The wife of Lithuanian rider Raimondas Rumsas is arrested after French police find doping substances in the boot of her car. Edita Rumsas says the stock, which includes testosterone, EPO and anabolic steroids, is for her sick mother.
" Rumsas, who finished third in the Tour, denies his wife obtained doping products for him and that he ever took any.
2003 Giro d'Italia
" Rumsas is suspended by his Lampre team in June after failing a drug test during the race in which he finished sixth overall.
2004 Tour de France
" Italian Stefano Casagranda and Slovenian Martin Hvastija are kicked out of the Tour on doping charges.
" Brit David Millar, France's Cedric Vasseur and Italian Danilo Di Luca are not allowed into the race for the same reason.
2005 Tour de France
" French police take Italian rider Dario Frigo in for questioning before the start of Stage 11 in the Alps after finding performance-enhancing drugs in a car driven by his wife.
2006 Tour de France
" Top riders, including Ivan Basso and Jan Ullrich, are kicked out of the race one day before the start in Strasbourg for their involvement in a blood-doping scandal known as "Operacion Puerto."
" Tour winner Floyd Landis tests positive for synthetic testosterone after an impressive solo effort gave him a Stage 17 win.
2007 Tour de France
" Spanish rider Iban Mayo, who finished 16th overall in the race, is suspended by his Saunier Duval team after cycling's governing body confirm traces of EPO in a
sample taken on the July 24 rest day.
" Michael Rasmussen is sacked by Rabobank on July 25 while leading the race after the Dutch team says he lied about his training whereabouts in June, an allegation the Dane denies.
" Cofidis announces on July 25 it is pulling out of the Tour following Italian Cristian Moreni's positive test for testosterone.
" Pre-race favorite Alexandre Vinokourov tests positive for blood doping after winning a time trial on July 21. The Kazakh's Astana team leaves the Tour and sacks Vinokourov, who denies any wrongdoing.
Information from Reuters was used in this report.