America's Tyler Hamilton has had his appeal against a two-year ban for doping rejected by the Court of Arbitration for Sport (CAS).
Hamilton won time-trial gold in Athens
Hamilton, 34, tested positive for blood transfusions at the 2004 Tour of Spain, weeks after winning Olympic gold.
He had given a similar positive test in Athens, but escaped sanction when the "B" sample was frozen and destroyed.
"The US Anti-Doping Agency proved its tests... were undertaken in the approved manner," said a CAS statement.
The US Anti-Doping Agency imposed a two-year ban on Hamilton, who won time-trial gold in Athens, last April, but Hamilton said the test used was unreliable.
A blood transfusion allows athletes to increase their oxygen-rich red blood cells, thus increasing aerobic power and endurance.
CAS confirmed that the ban started not in April, but in September, when Hamilton accepted a provisional suspension.