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BEIJING, Aug 2 -- Test show that some of the testosterone in Floyd Landis’ system at the Tour de France was synthetic and not naturally produced by his body as he claimed, according to a newspaper report.

    The French antidoping lab testing the American cyclist’s samples determined that some of the hormone came from an external source, The New York Times reported on its Web site Monday night, citing a person at the International Cycling Union with knowledge of the result.

    The finding undermines the defense that Landis has stood behind since he tested positive for an elevated ratio of testosterone to epitestosterone following the 17th stage of the Tour de France, where he staged a stirring comeback in the Alps to make up for a poor performance the day before.

    Looking and sounding defiant, Landis said Friday that his body’s natural metabolism — not doping of any kind — caused the result, and that he would undergo tests to prove it.

    But after determining that Landis’s ratio of testosterone to epitestosterone was more than twice the limit of 4:1, the lab performed a carbon isotope ratio test on the first of Landis’s two urine samples to determine whether it’s natural or synthetic, the Times said.

    Landis officially requested the testing of his backup urine sample Monday for an elevated testosterone ratio, and results were expected sometime this week.

    If the “B” test is negative, Landis would be cleared. If it’s positive, which Landis’ lawyers say they expect, he could be stripped of his Tour victory and banned for two years.

    Testosterone is a naturally occurring male hormone that is banned when it is found in a ratio greater than 4:1 to another hormone, epitestosterone.

    Oscar Pereiro of Spain, who finished second overall in the Tour de France, would be declared the winner if Landis loses the Tour de France title. It would be the first time in the history of the Tour de France that the winner has been disqualified for doping.